Nonsense.  This happens regularly in QBD when editing rules, not creating them.  The first few are fine and then it slows to a crawl the more rules you edit.  Close the file and reopen it, and you can edit a few more before it slows again.  This is endemic with QB Desktop and happens on every file I work on right up to QB 2021 (the latest version).  Whatever the cause, it needs a fix