Debian 12 upgrade: The most likely issue you are having is the firewalld configuration

Given the recent surge of reports pertaining to problems experienced during the FreedomBox upgrade to Debian 12, a common pattern seems to be emerging. The main issue appears to stem from changes made to the /etc/firewalld/firewalld.conf file during the upgrade process.

If you’re currently facing difficulties with your upgrade, please first verify the state of this particular file. Please, follow the suggestion made by @Avron in this previous post: