Direct upgrades from N to N+2 is not supported. You ought to have first upgraded to Bullseye then to Bookworm. If you have a backup of the Buster image you could go that route and it should work, unless you have some "non-standard" things installed which would be documented in both the Bullseye and Bookworm release notes.
I tried this in the past and it blew up spectacularly...then I read the documentation.
a couple of months ago I updated Debian from Buster to Bookworm and my
roundcube/dovecot installation stopped working.
Apache just presented a directory listing and my index.html link to the
roundcube install displayed a config file.
I thought I should get around to fixing it but put it off.
Just now I thought I'd get a raspberry Pi and reinstall everything on
that as they are smaller things.
I'll just look one more time
and... it's working.
I didn't do anything, haven't rebooted it.
What could that be?
Browser cache, DNS sorting itself out, some automatic update?
It is disturbing it just started working on its own.
mick