After a waiting a few hours last night, I forced the Sonos app quit. Tried installing a few more times, and it consistently hung with the progress bar at 100%.
Just now, I tried updating on another older secondary Mac that I sometime use with Sonos, and the update completed OK. Back on my newer/main computer, same hang.
Then, I deleted the app, downloaded a new copy, installed, and it seem to work. So, now I’m back to where I was a few days ago.
But, when I tried to reconnect my iTunes music library or the external/network drive where I have a large archive of music as FLAC, I get the same error that started with catastrophic Sonos app update a few months ago. So, I still don’t have the full functionality that used to make me very happy with my network of Sonos devices. Hopefully, there is yet another bug-fix coming soon.