It doesn't help that your system still is running the backports Debian 10/OMV 5.x kernel but I would try moving apparmor=0 to the GRUB_CMDLINE_LINUX_DEFAULT="quiet" line in /etc/default/grub and run sudo update-grub again.
I have already tried that, same result.
How do I fix the issue of still running the backports Debian 10 kernel?
Backports is checked in OMV-Extras->Settings, that is not something I checked on purpose.
Is it as simple as that, I just don't want to cause a boot issue, as I am not on same site as machine.