added options to build with to avoid removing and re-adding stuff

devices/desktop/default.nix

@@ -1,6 +1,7 @@
 { config, pkgs, ... }: {
   imports = [
     ./hardware-config.nix
+    ./options.nix
   ];
 
   networking.hostName = "desktop";

devices/desktop/options.nix

@@ -0,0 +1,5 @@
+{ ... }: {
+  withNiri = false;
+  withGnome = true;
+  withVM = false;
+}

devices/surface/default.nix

@@ -1,6 +1,7 @@
 { pkgs, ... }: {
   imports = [
     ./hardware-config.nix
+    ./options.nix
   ];
 
   networking.hostName = "surface";

devices/surface/options.nix

@@ -0,0 +1,5 @@
+{ ... }: {
+  withNiri = false;
+  withGnome = true;
+  withVM = false;
+}

modules/system/default.nix

@@ -2,16 +2,23 @@
 # your system.  Help is available in the configuration.nix(5) man page
 # and in the NixOS manual (accessible by running ‘nixos-help’).
 
-{ pkgs, ... }: {
+{ pkgs, lib, config, ... }: {
+  options = {
+    withNiri = with lib; mkEnableOption "Enable niri";
+    withGnome = with lib; mkEnableOption "Enable gnome";
+    withVM = with lib; mkEnableOption "Enable VM related configuration";
+  };
+
   imports = [
     ./audio.nix
     ./containers.nix
     ./fonts.nix
     ./gnome
     ./niri
+    ./virt.nix
   ];
 
-
+  config = {
     # Allow packages from nixpkgs
     nixpkgs.config = {
       allowUnfree = true;
@@ -78,4 +85,5 @@
       description = "twoneis";
       extraGroups = [ "networkmanager" "wheel" ];
     };
+  };
 }

modules/system/gnome/default.nix

@@ -1,4 +1,4 @@
-{ pkgs, ... }: {
+{ pkgs, lib, config, ... }: lib.mkIf (config.withGnome) {
   # Enable the GNOME Desktop Environment.
   services.xserver.displayManager.gdm.enable = true;
   services.xserver.desktopManager.gnome.enable = true;

modules/system/niri/default.nix

@@ -1,3 +1,3 @@
-{ ... }: {
+{ lib, config, ... }: lib.mkIf (config.withNiri) {
   programs.niri.enable = true;
 }

modules/system/virt.nix

@@ -0,0 +1,5 @@
+{ lib, config, ... }: lib.mkIf (config.withVM) {
+  virtualisation.libvirtd.enable = true;
+  programs.virt-manager.enable = true;
+  users.users.twoneis.extraGroups = [ "libvirtd" ];
+}