ARFI also wonder - will a 4-core / 8-thread CPU or APU be good enough to run Fortnite smooth?

8 Thread could be enough for most of esport titles. Your problem could be the 2500U CPU that has strong TDP limit. U means Ultra low TDP for ultra thin notebooks. Basically you have 15W TDP limit.

You architecture Zen 4c/8T and Vega 8 with Desktop 65W TDP or with unlocked TDP could provide a good gaming feeling, but with 15W limit... Only for low spec gaming.

ValantarHDPlex has the PSU for you. Other than that, that is exactly the GPU I want to see as well.

THX the suggestion, I know the brand, but It is overpriced way too much that is worth. I Bought my very good 80+ Gold PSU (near to 80+ Platinum efficiency) for almost half the price. That is why I want 200W high efficienty PSU from mass producers. I do not want so spent 2x money for a PSU. That would be nonsense.
Green and energy efficient PC should be common consumer product.

TomorrowGood. Atleast one company is providing perf per/w gains.

I bought an injured notebook, i5-5300U, 8G, 500Gb SSHD for overall ~ 60 EUR. I messured the avg. power consumption with wall plug power meter of browsing the web, watch youtube 1080p. Only 14-15W avg. Not fast, but not slow PC for this purpose, It is OK.
Overall There is no any dekstop PC that will consume this low 15W avg. during this usage. (Maybe if you build a PC with iGPU and Pico PSU to keep efficiency high as possible.)

Most efficienct modern PCs with dGPU consume at least 25-30W on Idle, when you just watching windows desktop.... If you browsing the web it will go up easily between 35-50W avg. or more.
(typical if you move the mouse without stop that could instant push up the CPU load by 6-12% so the CPU (and I have 6/12 10400f) never will be idle if you moving the mouse while scrolling and reading the web and watching youtube...)

For basic usage with low energy consumption maybe a good choice to buy a cheap ARM SBC or maybe an android PC, but this one has few limitation because of android TV OS, Or change the mobile phone to a Samsung DEX compatible smartphone.
Some recommendation.

kiakkTHX the suggestion, I know the brand, but It is overpriced way too much that is worth. I Bought my very good 80+ Gold PSU (near to 80+ Platinum efficiency) for almost half the price. That is why I want 200W high efficienty PSU from mass producers. I do not want so spent 2x money for a PSU. That would be nonsense.
Green and energy efficient PC should be common consumer product.

It's not overpriced, it's just low-volume specialty hardware aimed at a high-paying niche, using expensive components to achieve a very compact design. But I definitely agree with your desires - I really, really wish there were high efficiency 250-400W PSUs on the market in traditional form factors. Though the spiky power draw of modern GPUs complicates this a bit, most gaming PCs consume 200W or less under load, and really don't need 500W+ PSUs, let alone the regularly recommended 750W+. This is part of why ATX12VO had me a bit excited - it has the potential to drastically simplify cheap PSU designs, allowing for much higher efficiency at lower costs due to simplifying the design. Sadly 12VO for DIY seems entirely dead. The best option for high efficiency low output PSUs for now seems to be refurbished Platinum or Titanium server/FlexATX PSUs, but those are a whole other can of worms in terms of reliability (a lot of shady "refurbishers" that just clean and resell PSUs that have been hammered in a server rack for years), and they invariably need fan modifications to avoid server-grade noise.