I want to thank Phil (and Kai) for making this script.
The change from Bullseye to Bookworm ruined my mail server too, I did this on Thursday .. and my server's 12 users have not been able to access their email since. I have only run the script for 1 of these, as I was hoping that the Debian and or Cyrus developers would have something else.. I can still restore something from backup made a few hours before the change.
Kai explained he tried reconstruct, and removing of newly created mailboxes...
So ... Is this script really our only recourse?