So, it seems my specialization of NixOS config with nvidia drivers enabled tries to disable itself on nixos-rebuild switch. Kinda makes sense how it works but it sucks if I want to, I don't know, install some games and don't want to reboot for that?

"Fix" is kinda there, either manual switching in some obscure part, of nixos-rebuild flag, but first didn't work for me for unknown reason and second is only in unstable (I'm currently feeling pretty content with versions stable channel of nixpkgs provides, so I didn't try switching)