after installing apparmor (apt install apparmor) everything works
fine.
Should apparmor be added as a dependency to the lxd package?
That is interesting -- I've opened a bug with the upstream developers
(https://github.com/lxc/lxd/issues/10560) with some additional details
as I was able to reproduce the issue as well.
Regarding making apparmor a dependency for LXD, it is currently
recommended in d/control, which I think is correct, based on my reading
of Policy Chapter 7.2. Upstream does state that apparmor is an optional
feature of LXD, which is why I listed it as a Recommends, and not a
Depends. If there's consensus that the LXD package should depend on
apparmor, that's an easy enough change to make.