nix flake for build a single package from nixpkgs, this builds an unfree package.

gistfile1.txt

{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-21.11";
  };
  outputs = { self, nixpkgs }:
    let
      myNixpkgs = import nixpkgs { config.allowUnfree = true; system = "x86_64-linux"; };
    in
    {
      packages.x86_64-linux.cudaThing = myNixpkgs.python3Packages.tensorflowWithCuda;
    };
}