Greetings,
While I am only new to foreman, I have been trying Foreman 2.1.0rc{1,2,3} on CentOS 7 & 8. I can report that foreman-maintain's backup facility will currently not back up a Foreman-only system on either CentOS 7 or CentOS 8.
It seems and I could be wrong (but the documentation I read before posting about it, suggested otherwise), that foreman-maintain's backup facility will currently only backup systems based-on/using Katello (the content life-cycle management plugin). So if your just a Foreman user, Debian may not be your only issue.
My post on this ("foreman-maintain backup" fails on CentOS8 / Foreman 2.1.0rc* - Multiple Issues) didn’t get any responses.
Regards,
Peter