Any games that you can just run on Steam without issue will work fine, it’s when you have to start passing launch commands etc that things become more complicated. Most things are still possible but harder because you have to deal with the very unusual way Nixos stores its files. The specific thing that made me give up and go to CachyOS was trying to get gamescope working under wayland – every way I tried, I was having to compromise on what I actually wanted. Also VR has been easier to play with, though it’s still far from Windows parity.