made some progress

modules/nixos/desktop/gamescope/default.nix

@@ -0,0 +1,27 @@
+{ lib, config, namespace, inputs, ... }:let
+  inherit (lib) mkEnableOption;
+
+  cfg = config.${namespace}.desktop.gamescope;
+in
+{
+  imports = [ inputs.jovian.nixosModules.default ];
+
+  options.${namespace}.desktop.gamescope = {
+    enable = mkEnableOption "Enable Steamdeck ui";
+  };
+
+  config = mkIf cfg.enable {
+    "${namespace}".desktop.kde.enable = true;
+
+    jovian = {
+      steam = {
+        enable = true;
+        autoStart = true;
+        user = "chris";
+        updater.splash = "steamos";
+        desktopSession = "plasma";
+      };
+      steamos.useSteamOSConfig = true;
+    };
+  };
+}