Use modules folder

modules/picom/default.nix

@@ -0,0 +1,28 @@
+{ ... }:
+
+{
+  services.picom = {
+    enable = true;
+    settings = {
+      backend = "glx"; # Fixes black backdrop on some rounded corners
+      corner-radius = 12;
+      round-borders = 1;
+      blur = {
+        method = "gaussian";
+        size = 8;
+        deviation = 2;
+      };
+      blur-background-exclude = [
+        "override_redirect = true"
+      ];
+      # Ignore polybar
+      rounded-corners-exclude = [
+        "window_type = 'dock'"
+        "window_type = 'desktop'"
+      ];
+      opacity-rule = [
+        "0:_NET_WM_STATE@:32a *= '_NET_WM_STATE_HIDDEN'"
+      ];
+    };
+  };
+}