Fixed

flake.nix

@@ -15,9 +15,13 @@
       url = "github:AvengeMedia/dgop";
       inputs.nixpkgs.follows = "nixpkgs";
     };
+    niri = {
+      url = "github:sodiboo/niri-flake";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
   };
 
-  outputs = { self, nixpkgs, home-manager, dms, dgop, ... }@inputs:
+  outputs = { self, nixpkgs, home-manager, dms, dgop, niri, ... }@inputs:
     let
       settings = import ./settings.nix;
       system = "x86_64-linux";
@@ -29,6 +33,7 @@
         ./configuration.nix
         home-manager.nixosModules.home-manager
         dms.nixosModules.greeter
+        niri.nixosModules.niri
       ];
     };
   };

modules/desktop.nix

@@ -4,8 +4,9 @@ let
   settings = import ../settings.nix;
 in
 {
-  # Niri compositor
+  # Niri compositor (use nixpkgs package for 25.11 compatibility with DMS)
   programs.niri.enable = true;
+  programs.niri.package = pkgs.niri;
 
   # DankGreeter display manager
   programs.dank-material-shell.greeter = {