This video should answer a few of your questions

He has been summoned

In my case, it just worked, on two machines. Just added steam and lutris into the config along with two other options recommended for gaming and it worked.

Once you installed steam you should be fine to go for the most part. Installation is however more like an enable in the configuration.nix

I recommend protontricks and protonupQ.

Then most should work. If you have a Linux game that you don't want to run through steam you can use the steamRun command in nixos if it has issues finding libs.

I haven't tested lutris and the hero launcher though.

However running epicgames through steam works fine.

I haven't tried it out yet for some reason, but I'd start here https://youtu.be/qlfm3MEbqYA

Search the manual for support32Bit configuration options, like hardware.opengl.support32Bit, hardware.pulseaudio.support32Bit, or services.pipewire.alsa.support32Bit. Any 32-bit games, as well as Steam itself, will need these to get their GL and PA/ALSA libraries set up properly.

You may also want to look up what programs.nix-ld.enable does, although I hear that there's a better harness builtin as of NixOS 24.05.

All that said, everything Just Worked when I last tried. I haven't run Steam in a while, though. I do use Retroarch and OBS without problems, though, streaming PS4 speedruns to Youtube or Peertube, and that all works out-of-box.

Works pretty well for me. I just have this config:

  # Sadly we can't easily install steam on a per-user basis, because installation
  # requires touching a lot of system libraries, etc.
  programs.steam = {
    enable = true;
    remotePlay.openFirewall = true; # Open ports in the firewall for Steam Remote Play
    dedicatedServer.openFirewall = true; # Open ports in the firewall for Source Dedicated Server
  };

I'm using Sway on an Nvidia RTX 4080 Super. It's important to be on the latest driver. I'm still waiting for Sway to merge support for DRM explicit sync objects, but until then, gaming still works fine with the occasional artifacts from lack of synchronization with the kernel.

If by chance you need a specific Nvidia driver, you can configure that like so:

  hardware.graphics.enable = true;
  hardware.nvidia = {
    package = config.boot.kernelPackages.nvidiaPackages.stable;

    # More versions readily available for downgrading.
    # package = config.boot.kernelPackages.nvidiaPackages.mkDriver {
    #   version = "535.154.05";
    #   sha256_64bit = "sha256-fpUGXKprgt6SYRDxSCemGXLrEsIA6GOinp+0eGbqqJg=";
    #   sha256_aarch64 = "sha256-G0/GiObf/BZMkzzET8HQjdIcvCSqB1uhsinro2HLK9k=";
    #   openSha256 = "sha256-wvRdHguGLxS0mR06P5Qi++pDJBCF8pJ8hr4T8O6TJIo=";
    #   settingsSha256 = "sha256-9wqoDEWY4I7weWW05F4igj1Gj9wjHsREFMztfEmqm10=";
    #   persistencedSha256 = "sha256-d0Q3Lk80JqkS1B54Mahu2yY/WocOqFFbZVBh+ToGhaE=";
    # };
    # package = config.boot.kernelPackages.nvidiaPackages.mkDriver {
    #   version = "550.40.07";
    #   sha256_64bit = "sha256-KYk2xye37v7ZW7h+uNJM/u8fNf7KyGTZjiaU03dJpK0=";
    #   sha256_aarch64 = "sha256-AV7KgRXYaQGBFl7zuRcfnTGr8rS5n13nGUIe3mJTXb4=";
    #   openSha256 = "sha256-mRUTEWVsbjq+psVe+kAT6MjyZuLkG2yRDxCMvDJRL1I=";
    #   settingsSha256 = "sha256-c30AQa4g4a1EHmaEu1yc05oqY01y+IusbBuq+P6rMCs=";
    #   persistencedSha256 = "sha256-11tLSY8uUIl4X/roNnxf5yS2PQvHvoNjnd2CB67e870=";
    # };

    modesetting.enable = true;
    nvidiaSettings = true;
  };

  # Weird that "xserver" is here when we are using Wayland. But this is required
  # to install the NVIDIA driver.
  services.xserver.videoDrivers = [ "nvidia" ];

Some games don't work, despite what ProtonDB says, such as Stardew Valley.