Nah, dotfiles is fair, it would be insane to put it in only one file, it is Kore like a flake.nix that glues a bunch of configuration files together :P
I've had to do very little tweaking overall to get most games working, with the one notable exception being dragons dogma 2. The solution was proton GE and a new .nix file with GPU tweaks and now I'm getting slightly better performance than the average windows experience.
I have to admit, that I have some experience with nix on 2 servers and 1 desktop, but installing steam was just 1 line in the config and everything worked. My biggest concern were the nvidia drivers, but that worked as well. Currently playing RE4 Remake.