This is an duplicate of #1102751. Apparently ceph-mgr uses subinterpreters and the native code of python3-bcrypt doesn't support this. previous versions allowed this silently, but with trixie this was turned into an Exception. In upstream Ceph this was fixed a year ago[1], but there hasn't been an backport of this fix.
[1]: https://github.com/ceph/ceph/pull/62951
