Comment 6 for bug 1833040

In a Eoan VM I can recreate your case (with peer = libvirt without path)

I was discussing with jjohansen, but we couldn't easily identify a apparmor related change.
I'd think we actually have two cases here:
- there was some libvirt change that slightly changed how this is called
  - in LXD+HWE kernel this leads to no peer detection at all - but that is an unsupported corner
    case anyway, and might even be good with a newer kernel like the one you have
  - in normal execution the peer detection changed from "/usr/sbin/libvirtd" to "libvirtd"
  - the latter might be depending on the kernel, so e.g. UCA backports might see the old one

Ha I found the change that triggered this and a partial cleanup:
Trigger: https://libvirt.org/git/?p=libvirt.git;a=commit;h=a3ab6d42
Partial cleanup: https://libvirt.org/git/?p=libvirt.git;a=commit;h=4ec3cf9a

Ok, the needed change is clear let me suggest it upstream.