nixpkgs.system

This option does not need to be specified for NixOS configurations with a recently generated hardware-configuration.nix.

Specifies the Nix platform type on which NixOS should be built. It is better to specify nixpkgs.localSystem instead.

{
  nixpkgs.system = ..;
}

is the same as

{
  nixpkgs.localSystem.system = ..;
}

See nixpkgs.localSystem for more information.

Ignored when nixpkgs.pkgs, nixpkgs.localSystem or nixpkgs.hostPlatform is set.