Just so it’s clear for everybody: Nix is a programming language, build system, and package manager. NixOS is a Linux distro built with (and upon) Nix. Home Manager is a dotfile and home management tool using Nix, allowing control of dotfiles, but also per-user software, systemd services, and more. You can use Home Manager in any distro, not just NixOS (but you do need to install Nix).
I’ve played Skyrim and Fallout 3 & 4 on Linux, and Uncharted. They worked just fine.
You need to enable Proton for all ‘unsupported’ titles in Steam (literally two clicks). After that…the only games I’ve found that don’t work are down to anti-cheat. I used to occasionally have to change the Proton version for some games, but it’s been a while since I had to do that.
It’s nothing like gaming on Linux was 10 years ago. It’s much more like gaming on Windows, the last time I did it: you occasionally find a game that needs tweaking, but 95% work flawlessly.