We use PG 11.9 and are encountering the problem with connection limit and parallel workers aborting a totally valid query ("CONTEXT: parallel worker" error)
Do you know the status of the patch or a modification to remove the parallel worker from the connection count against user (also server?) CONNECTION_LIMIT or to just not launch workers if not possible?
That thread was resolved with a committed patch [1] mid-thread, then got hijacked a bit...