NVIDIA

Card type

MXM / output-providing card (shows as VGA Controller in lspci), i.e. graphics card in desktop computer or in high-end laptop
muxless/non-MXM Optimus cards have no display outputs and show as 3D Controller in lspci output, seen in most consumer laptops with nvidia hybrid graphics

MXM

Follow NVIDIA Graphics Cards section in official manual.

In case of laptop you may also need to use BIOS option to select which card to use for internal display or you're even forced to use external video port with some laptops.

Optimus

There are currently two solutions available under NixOS:

Bumblebee

Unofficial solution, but is easy to set.

Use

hardware.bumblebee.enable = true;

option.

Pros: out of box experience, just start the game via primusrun or optirun wrapper

Cons: some performance penalty, no Vulkan support, things like CUDA and OpenCL are problematic to configure

Nvidia PRIME

Official solution by nvidia, but needs some preparing.

1. Configure NixOS to allow Intel and Nvidia X.Org drivers coexist together, and also to disable nvidia card by default.

/etc/nixos/configuration.nix

let
  # nvidia packages to use
  nvidia = pkgs.linuxPackages.nvidia_x11;
  nvidia32 = pkgs_i686.linuxPackages.nvidia_x11;
in
{
  # disable card with bbswitch by default
  hardware.nvidiaOptimus.disable = true;
  # load kernel modules
  boot.extraModulePackages = [ nvidia.bin ];
  # install nvidia drivers in addition to intel one
  hardware.opengl.extraPackages = [ nvidia.out ];
  hardware.opengl.extraPackages32 = [ nvidia32.out ];
}

2. Use primerun script for out of box experience.

Like with Bumblebee, start the game via primerun.sh.

Pros: better performance, Vulkan is supported. CUDA and OpenCL should work, though CUDA needs an additional device creation rule https://github.com/NixOS/nixpkgs/blob/05e375d7103ac51e2da917965c37246c99f1ae4f/nixos/modules/hardware/video/nvidia.nix#L72

Cons: there are still some rough edges noted on the top of script, but otherwise it works fine for me