OK, things are working now on my MacBook Pro as well as Mac mini.
(1) After looking up how to remove the drivers I discovered they weren't installed in the first place. Trying the installer again, it fails under Sonoma 14.4.1 (23E224). But it turns out it's not needed.
(2) I'm not sure how I missed it, but the answer was here:
https://github.com/BelaPlatform/Bela/wiki/Getting-started-with-Bela#troubleshooting---macos
Making the needed changes in the Preferences/Network control panel did the trick. And apparently I only needed to do this the one time. It seems to remember from one login to the next.
Thanks for your help, and I apologize for overlooking what I should have tried in the first place.