nixos/modules/system/gui.nix

inputs:
{
  config = inputs.lib.mkMerge
  [
    # enable gui
    (inputs.lib.mkIf (builtins.elem inputs.config.nixos.model.type [ "desktop" "server" ])
    {
      services =
      {
        displayManager =
        {
          sddm = { enable = inputs.lib.mkDefault true; wayland.enable = true; theme = "breeze"; };
          defaultSession = "plasma";
        };
        desktopManager.plasma6.enable = true;
        xserver.enable = true;
      };
      environment =
      {
        sessionVariables.GTK_USE_PORTAL = "1";
        persistence."/nix/rootfs/current".directories =
          [{ directory = "/var/lib/sddm"; user = "sddm"; group = "sddm"; mode = "0700"; }];
      };
      xdg.portal.extraPortals = builtins.map (p: inputs.pkgs."xdg-desktop-portal-${p}") [ "gtk" "wlr" ];
      i18n.inputMethod =
      {
        enable = true;
        type = "fcitx5";
        fcitx5.addons = builtins.map (p: inputs.pkgs."fcitx5-${p}")
          [ "rime" "chinese-addons" "mozc" "nord" "material-color" ];
      };
      programs.dconf.enable = true;
    })
    # prefer gui or not
    (inputs.localLib.mkConditional (builtins.elem inputs.config.nixos.model.type [ "desktop" ])
      { environment.sessionVariables.NIXOS_OZONE_WL = "1"; }
      { environment.plasma6.excludePackages = [ inputs.pkgs.kdePackages.plasma-nm ]; })
  ];
}