If I create a backup with the Zammad script on CenOS7 (file and PostgreSQL 14) and restore it on a newly set up Ubuntu 24.04, do I have to reinstall all applications, create users, firewall settings … or is it all on the backup and will therefore also restored?
Not sure what your question actually is.
If you use Zammads backup and restore to migrate to a new system, yes of course you will have to run the minimum installation stuff. Zammad configurations are (as outlined in our documentation) restored with exception for performance tunings.