/enums/audience_insights_dimension.proto 

--- v20/enums/audience_insights_dimension.proto 2025-08-05 14:39:36.000000000 +0000
+++ v21/enums/audience_insights_dimension.proto 2025-08-05 14:39:44.000000000 +0000
@@ -78,5 +78,8 @@

     // A YouTube Lineup.
     YOUTUBE_LINEUP = 16;
+
+    // A User List.
+    USER_LIST = 17;
   }
 }