Hi @yoursql719 - good question! Surely we will support Debian 11 but our packaging service packager.io doesn’t support it (yet).. There’s the possibility to contribute the support. We haven’t had the need for it yet and are focusing all of our resources to the upcoming 5.0 release.
Once packager.io supports Debian 11 it’s pretty straight forward to add support in Zammad as well. We’re also happy to receive contributions 
Hope this helps!