nixos/system/steam.nix

{ username, ... }:
{
  hardware.steam-hardware.enable = true;
  programs = {
    gamemode.enable = true;
    steam = {
      enable = true;
      remotePlay.openFirewall = true;
      gamescopeSession.enable = true;
    };
    gamescope = {
      enable = true;
      capSysNice = true;
    };
  };
  home-manager.users.${username}.programs.mangohud = {
    enable = true;
    settings.preset = 1;
  };
}