Hah! Yeeeahhhh.... been playing that one lately, too. I know just how much of a buggy mess it can be, and just to up the ante I'm running a few hundred mods! Honestly it's a wonder it's playing well at all.
The lag and general unresponsiveness has a few causes. Some of them are fixable, others are just god awful optimization. Like, that game is so poorly optimized that it STILL stutters if you're pushing it with a 2080ti and say 9900k
It will be 10 years at least before the hardware to run Fallout 4 completely smoothly arrives.
There are some mods that can really do a lot to help... better optimized texture packs, fog removal, insignificant object removal... I'm sure there are more that I'm forgetting. And then there's the Unofficial patch which fixes many causes for gameplay instability, bad NPC behaviors, broken quests... just a whole slew of things. Would highly recommend at least looking into that one. I can say that even with all of my heavy mods, ReShade AND ENB, the game actually runs pretty smooth. Believe it or not, if your PC can handle them, many mods make the game run better by coincidence. Don't ask me how that works. I just know that if I disable all of my mods and run it completely vanilla, it's nowhere near as smooth. The only thing hurting me are the post-fx I add. Turn those off and the game is surprisingly responsive the vast majority of the time. Running a lot of 4k textures and everything. Though honestly it generally runs very good with everything piled on now. But there was a long here-to-there in-between. It's a very touchy system. Kinda like that old beater station wagon that just keeps on going for years and years, rust and busted window mechanisms and all. But you know the frame underneath is rusted out and one wrong bump will have you skating on the chassis. So you're very particular about driving and working on it.
There are a million settings tweaks you can try, too. But you'll have to look into it yourself. It gets very specialized... some folks out there have dug deep. I just recently found one that fixed a lot of my texture pop issues via unlisted ini settings. Some absolutely require direct ini edits, though there are also a couple of ini editors out there that give you a GUI for many of the settings vital to performance. Personally I've been using bethini for generations of bethesda games and it has never done me wrong. None of the settings it gives you have the potential to break things. There's a fair chance you can fix most of the lag messing around in there. First step would probably be to cut off the more detailed LOD levels far sooner (bethesda's 'medium' LOD setting rivals many modern games' 'ultra' LOD setting.) And for christs sake disable those godrays. They are just broken in places and will tank performance in many areas of the game. Not to mention they look awful. Have you ever seen horrible, mosaic-esque blocky edges on objects under volumetric lighting? That's why. Also lower shadow quality/distance. The shadow system is so badly optimized in that game and honestly they look bad even if you max them, so no loss turning them way down. The performance hit in areas with lots of buildings/objects is huge because of shadows. And I promise you won't miss having them turned up. Everything looks pretty much the same type of blocky and your global shadows are fixed anyway. It's the local ones you have settings for that cause problems.
Another one I'd recommend installing under the hood is FO4 Load Accelerator. Basically it gives you a modified DX .dll file and an ini to drop into the game directory which only serves the purpose of disabling vsync on the loading screens, making them go much, much faster. Get this... load times in FO4 are tied to frame rates! Figure that one out. And you can't just disable vsync... the physics and scripted movements start to break beyond 60fps. Another thing to watch out for... many people have stuttering problems with vsync. Tends to be a problem when you're having trouble holding 60fps. Can't help you if that's part of your problem, I've never dealt with that. But my understanding is that you need to disable in-game vsync and use your card's adaptive/dynamic vsync instead. Reason obviously being the lag caused by running vsync below target FPS. It needs to shut off whenever that happens. Unfortunately the load accelerator will no longer work, then.
Others may recommend to disable vsync entirely and just run a cap. I wouldn't unless you're immune to profound tearing the moment your machine starts coughing up more than 60 frames. At that point it's probably gonna be much better to try and get frame rates consistently at or above 60 and use regular vsync.
Another fix for poor performance is F4SE. At heart, it simply extends the script library to give extra functionality for some mods. But it also replaces/streamlines some problem scripts used by the base-game, as was coincidentally needed for certain mods to function effectively. So even if you don't run mods, it might be worth installing just to ease some backend load.
Yet another silly thing that works with many other games is going from fullscreen to windowed/borderless, depending on where you're at. Most people get better performance with one and not the other, but which it is varies from setup to setup with FO4. Another semi-related thing is to set the process to 'always active' which keeps the game fixed at a higher priority. All easily accessible through bethini.
The collision is terrible... it's like the boundaries have half of the polygons. So any point of converging or diverging lines is liable to have invisible barriers cast around it. No way to fix that :/ Well... save for going in and editing EVERY static object in EVERY sector of the worldspace... daunting to be sure. And it's not even that simple. FO4 uses precombines - a way of combining the geometry of neighboring static meshes into what the game then sees as one object. Say you have a stack of 7 or 8 tires with unique meshes. Thanks to precombine you don't need seperate drawcalls for textures, polygons, shadows, and collision of each mesh. Only the one of each for the final 'tethered' version that spits out all of the geometry at once. Though that is to say the collision data is baked-in too. And unfortunately if you alter anything in a precombine, performance actually breaks completely... because previs (basically runs predetermined code against player head orientation and precombine data to figure out what is visible and therefor rendered - so that it's not rendering sides of say... walls, trees, and such, that you can't see from where you are) is also dependent on it.
Force those out, and you'll be lucky to see 20fps in areas where this has happened... even luckier if it doesn't crash your game and even corrupt your save the moment you walk into the area it's in. At best, your drawcalls multiply by 5x and the game just slows to a crawl. The object itself is like a medusa head, locking you in the moment your eyes meet it. The game basically flips a bitch and turns both systems off at the first sign of trouble, which is good in that the game really truly doesn't work on a low level when those run out of sequence - it needs them to run in a definite, manually-set manner... but I also think maybe they shouldn't be so easy to break? Or at least be easier to fix? It just seems primitive and inflexible for something so vital. Even when bethesda wants to change one simple thing in one part of the world space, they have to rebuild a whole bunch of these things or the game will fall apart, even in seemingly unrelated areas! Basically anywhere that modified object pops up, there is a dimensional shift.
Bethesda offers a tool for rebuilding them so you can remove/modify static objects safely, but it's much more primitive than the one they themselves use in-house... to try and make large-scale changes like that would take months of treating it like your night job. as you have to go object-by-object/cell-by-cell... it's a lot like getting your hair cut... one hair at a time. There's no reason why it can't do regions in batches by looking at where they've been turned off by modifications and simply recompiling them as the systems expect. In fact, there's no reason why this can't be coded to run dynamically, as it does and did in virtually every other game using that system back then. It's not even about modding, but rather because the amount of time it takes devs to build and make changes to the world as the go about actually making the game is multiplied exponentially if they have to manually go in and set those parameters up each and every time. Bethesda just hasn't gotten around to it yet... which at this point they're closer to a decade late to the party than not.
Actually, that's also part of why some places just lag... the whole system is poorly set-up. The governing regions for different sectors are poorly divided. I mean... like really haphazardly split. I think the layouts changed drastically between when they drew the lines and now so that there's a bunch of overlap. Probably decided that it's not worth the monumental time needed to fix it, since it does work decently well as-is... even if it's terrible practice by current optimization standards, and was then. And again, in all of this time nobody has managed to fix it because it is humanly impossible to do so before the next real Fallout title is released, whenever that is. It's like diffusing a bomb. And when you cut the wrong wire, the whole process of figuring out what went out and how to fix it is convoluted as all hell. You'd have to be crazy, or have several months of amphetamines on-hand. Probably both. Let's go with that.
Well... they could have fixed it in all of the updates they've pushed out. But instead of fixing bugs and optimizing the game better, the updates mostly serve to add creation club content that nobody buys into. The added benefit is that every time they do, a bunch of memory entries change arbitrarily and it makes any mods accessing them cease to work until the author picks up on it and updates their mod, which usually tends to be quite a lot of popular mods. We all love them for that, I'll tell you! Any serious modder disables automatic updates in steam and never launches the game from the steam launcher. But if you do accidently update it, rest assured somebody out there has found a way to trick steam into giving you the previous version!
Like... these games are just a mess under the hood man. You complain of lag... I'm just scratching the surface of FO4's issues.
And yes... you're understanding it right. If you so much as delete the wrong object, ONCE, from one SINGLE, ISOLATED LOCATION, it will actually BREAK the ENTIRETY of any other WHOLE REGION in the game with so much as ONE of those static objects in it. The most infamous there are trees. Certain trees, as forest-modders know too well, cannot be removed from anywhere without most of the outdoor areas completely tanking. If you've ever heard stories of mods breaking saves, those types of mods are nearly always the reason. It's not bad scripted mods... that doesn't really happen much in FO4... no. It's the damned trees! The TREES are destroying the universe!
I also recently dealt with one mod that changed a tire mesh that was part of a precombine... and anywhere there were static tire piles, the game would either slow down or crash. Sometimes when fast-traveling in or going from an interior into one of the affected areas, the loading screen would just hang. Didn't even bother trying to rescue that save. I had to start over to even be able to diagnose which mod was doing it. All over a friggin tire, because some dude innocently didn't like the look and diligently worked to make it look better. Best part? It took me a solid year of running that mod to realize what the problem was. Do you appreciate how insane it is to have to isolate a whole game shitting on you to a friggin tire mesh?! How about a toilet? Or a footpath tile? To look around at a few hundred objects and pinpoint "Oh, all of the places where the game lags have a tire pile tucked away somewhere... I see they have nothing else in common." How many completely different areas in a post apocalyptic game do you think have those? A lot. How long d'you suppose it takes to become mentally unsound enough to deduce that? A long time, man... a long time.
You can imagine... if this is all that it takes to basically break the whole game, it mayyyy not be all that 'steady' to begin with
You can add as many things on top of the precombines as your clogged, swollen heart desires... build towering skyscrapers with 10000 objects inside... game doesn't care. Change a tire mesh or drop an ugly tree out and the world collapses. And the part that makes it really maddening is that it will come and go. You could have 4 long playthroughs with no game-breaking issues. And then at some turning point in that 5th playthrough, every 5th loading screen starts to hang and you get CTD's like nobody's business. This has lead many people to confuse the causes, but I suspect it's broken precombines most of the time, just going by all of the circular chatter based around these odd problems.
The damned settlers thing drove me crazy for the longest time. Why do they have to stand in that friggen sanctuary door all of the time?! There's a mod that is literally called
Move that fixes that. It basically makes it so the move sooner after you bump them and then when they do move, makes them move twice as far. Cheekily enough, they are coded to see when they're in your way. They just also happen to be instructed to ignore you for a while before inching a little bit in another direction. They're basically put there to be assholes and minorly inconvenience you everywhere they can. They actually do know exactly what they're doing...
There's also "Better Companions" which revamps companion behavior to fix many of the annoying little behavioral things I'm sure you have or will encounter as well as making them actually useful in stealth and combat. No longer will they spontaneously break stealth to run in with guns blazing with no obvious trigger. And when they do shoot, they hit things most of the time! As a bonus, they don't spaz-out and go sprinting off 100 feet like they just saw a rat at that exact moment when you become overencumbered and need to dump items on them. And dogmeat doesn't run in front of you and just stop as much. How do they miss this shit in QA? It's immediately annoying and I promise you nearly every tester experienced it. It'd be one thing if we were talking major changes to fix, but it's literally 5 minutes editing a few plain-text parameters. Most fixes for this games are only that.
Stuff like that is what got me into modding the game. So many little quality of life tweaks you can bring in to make the game so much more enjoyable. I started off simply fixing things. Then I went to upgrading the look. Once you're running a weather/lighting overhaul, water overhaul, foliage overhaul, and some quality texture mods, it's almost impossible to go back to vanilla, which in my estimation, has aged absolutely terribly. I can't man. ReShade and ENB only seal the deal... the former injects post-shaders while the latter hooks directly onto the rendering engine to put shaders behind the depth buffer, allowing quite a lot to be mixed-in. Between the two you have a lot of power over the game's look and can play around with different types of AA, LUT's, AO, lightroom/aftereffects-style adjustments, a million different kinds of sharpening, advanced DOF, bloom/ambient lighting with lens dirt, flares, all sorts of more "modern" touches. The type of stuff you'll see in games today with their 'ultra' presets.
My favorites these days are the gameplay mods. There are weapon overhauls which change the specs of the weapons to make them make more sense and make some of the cool, but useless weapons actually fun to use. And then there's stuff like Armorsmith which allows for much wider armor/clothing modding (in-game mods) and unlocks combinations that most people would say were arbitrarily and unsatisfying limited. The side-effect is that enemy armors get a little tougher... but I've also lowered their HP a little bit, so they drop quick (but not too quick) if you're appropriately leveled. Basically, weapons do more damage, so you bring down enemies quicker, but they can also drop you very quickly. Late-game can be such a grind, they become bullet sponges. I largely avoid that. To further spice it up I have a mod which makes the screen blur momentarily when shot. Between all of that, combat has actual energy and the weapons you use matter so much more. Even if you're overarmored, you still can't fight while being hit, so if you don't play it smart, you'll be the one getting whittled down! I routinely go to the wrong places ill-prepared and get my shit wrecked, on normal! Keep in mind I've put in 1059 hours - I know how to play the game as well as what is lurking where! On vanilla I could run through very hard like a god. Much more interesting when there are more weapons to choose from and combat has actual tension. Staying away from the harder difficulties also minimizes the bullet-sponge problem. Bethesda's idea of difficulty is a joke as far as that goes. That's the entirety of thier concept of it - ridiculously high enemy HP/defense. Meanwhile, their attacks stop scaling just like your weapon damage does. So it progressively becomes like an endless rock-em-sock-em robot dance. It feels like you're all just running around in costumes, limp-wristedly smacking each other with dirty wet socks. Not super fun or particularly difficult. Don't get me started on their 'survival' mode. It's such a gross misappropriation of what a good survival game is. Just... no. It's like a robot imitating human emotions. It's kinda like the real thing, but some things always remind you of how far off it actually still is.
I've also tried to make the game more rewarding. I upped global exp rate to 110%... not so much as to burn through levels, but enough to level at a pace where I've made decent progress up the perk tree before finishing the bulk of the main content and DLC... so you can actually USE those perks before you run out of shit to do other than run around doing radiant fetch quests, kill powerful monsters, and add more to your towering piles of weapons, armors, and junk. Legendary enemies also spawn a little more often. Chests and trunks all spawn a legendary weapon. And I changed the rate of melee-ballistic. Supposedly it's even by default, but I have done most playthroughs up past level 60 only finding ONE, SHITTY non-melee legendary for my gun-toting characters. Once the RNG locks-in on a certain pattern, it tends to repeat it throughout the entire playthrough! I'm not sure what they did with it, but it really jacks you in a majorly punishing way. Many people do several loooong playthroughs before they get a single decent one. And it's not like they're super-amazing to begin with. Like, the legendary weapons in this game are such a crapshoot they might as well not be there. It's nice to occasionally find one that I can use
And then there are all sorts of mods that add all-new weapons and outfits for you to find as you play the game. Those are honestly more fun. A lot of work and love goes into those weapons and outfits.
So I feel for you attempting to play through plain FO4. I couldn't do it these days... nuh-uh. I wouldn't fault anyone for being let down by the bare, unmodded game. A lot of things about it were never good, and at this point are egregiously bad. I still love playing the game, but so help me god, there is a loooonnng list of things, which if they do not change in thier next major title, will leave me with no choice but to not play it. I won't do it. Modding FO4 has been a monumental task... and it has been very rewarding, so much so that I'm spoiled beyond the point of no return. But to ever again put this much work and research into making a game play right... no. Nobody has that kind of patience... to spend weeks and months building up a mod setup, just to get reasonable enjoyment out... with each new game? It's simply too much. If I lost all of my backups and my whole mod setup went poof tomorrow, I would never pick up FO4 again. Being there is great. Getting there... sucks. It just sucks. At times, it can be fascinating just fixing things and learning about how it all works. But more often it is just as frustrating as the problems the game has sans-mods. It's gotten to a point where we are paying them for the privilege of finishing their games ourselves. Bottom line is, Bethesda is cheap. Ridiculously so. And I find that pretty sad, given the love people have for their games. It really is an abusive relationship, though.