This was already changed for Material nodetrees on duplication in rBa75ac18638f4. Since it is not obvious from the UI how change World actions - and to be consistent with Material actions, it is best to copy the action as the default behavior. So use generic BKE_id_copy functions with LIB_ID_COPY_ACTIONS flag [which also enables us to get rid of `BKE_world_copy`] Note: taking the User Preference `USER_DUP_ACT` into account here (for both material and world actions) could be a followup step. Maniphest Tasks: T81248 Differential Revision: https://developer.blender.org/D9046