You mean akin to main system memory usage on PC correct? If so I'm not sure how that translates over to console, if they can save space due to the memory being unified, ect. I don't know enough about game engines and how they work on console vs PC to know how that is handled. The only thing I can comment on is the observation that in step with games being made for the new consoles, PC requirements have also increased. Obviously these new games do work on the console so either they are very well optimized for console or PCs will simply require a lot more memory overall to makeup for the close to metal approach consoles take.
Microsoft have stated that Developers can only use 13.5GB total in the Series X, and yes that
does need to run the game too. 2.5GB are reserved for the OS and system functions and cannot, will not ever be available to game devs for either their game engine or as VRAM.
So realistically, the XBSX has 13.5GB of gaming RAM and the typical balance is 3.5GB game engine and 10GB for graphics, but that can go up to 12GB for lighter games and as low as 9GB according to devs commenting on Reddit. For the heavy-hitters that are crushing 8GB cards, we can assume that the game engines themselves are not lightweight, so it's a safe assumption that the XBSX is making do with 10GB or less.
Owing to focused, single-purpose hardware/driver/OS, the Consoles can get away with less VRAM though. DigitalFoundry have gone in to depth on "console equivalent settings" and for the latest round of games, you need 11GB+ of VRAM to run games without VRAM issues at XBSX settings, and those are likely games heavy enough to be dropping the XBSX to 10 or 9GB of VRAM. DF cannot be more granular than that because they only have 10, 11, 12, and 16GB cards to test with - the GPU VRAM amounts are fixed, rather than dynamic like on recent consoles.
I can imagine that if a game needing 12GB VRAM on XBSX ever gets a port to PC, then it could genuinely require either a 16GB GPU, or mandate something like DirectStorage on a 12GB GPU.
Edit - I forgot to mention that this is extremely unlikely as the XBSX has an asymmetric GDDR6 layout to give 10GB lots of bandwidth and the remaining 6GB has much less. So while a dev *can* use more than 10GB of VRAM on the XBSX, it's probably not worth the tradeoff to spill GPU allocation into the slower 6GB partition.
