Thank you, Eli.  I will try to look into this, when I get a chance.  I was just wondering if the whole misbehavior is connected to focus issues.  Meanwhile if I can provide more information about the other mystery, I would be happy to do so.  Emacs 31 mostly works OK on MacOS (once in a while it seems to forget to echo a character typed until the next character is entered and a few other oddities), but this new-frame behavior is annoying, as I have developed a habit, when I need to do something new and unrelated and perhaps short, to make a new frame, take care of things there and then remove the frame.  The current behavior is interfering with that.

–Boris