🇬🇧 How to regenerate the Apparmor config under Debian

How to fix „failed to connect to notification socket ‘/run/systemd/notify’: permission denied”?

TLDR:
I have just wrote a forum post on Proxmox about this very annoying issue.
https://forum.proxmox.com/threads/bind9-installation-fails-using-proxmox-9-0.171558/post-814074

Long story short: Old apparmor configs might influence your setup, just like mine.
Mine was restarting every few minutes with the error:
named: failed to connect to notification socket '/run/systemd/notify': permission denied