After I updated to kernel 6.4.11-1-default, every time I booted a LXC I was
getting this error:
“libvirtError: internal error: Unable to find ‘memory’ cgroups controller
mount” 

I replicated the installation in a minipc (Intel N5105) and it worked
perfectly, so I did a new installation in the first computer (AMD Ryzen 5600G)
and, again, I got the same error of the beginning. I tried in other two
computers (AMD Ryzen 5900X and Intel i5-1135G7) and I got the same error.

If I added “systemd.unified_cgroup_hierarchy=0” to the boot line, the error
went away, but it was really unstable (containers stopped working after a
while).

I usually install the tools of virtualization through Yast (KVM Server and KVM
tools). After that I install a few more packages: libvirt-client,
libvirt-daemon, libvirt-daemon-lxc, libvirt-daemon-driver-lxc,
system-user-libvirt-dbus. Finally, I add the user to groups libvirt, qemu and
kvm. Reboot and run.

The details of the error using Virt-Manager:

Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/asyncjob.py", line 72, in
cb_wrapper
    callback(asyncjob, *args, **kwargs)
  File "/usr/share/virt-manager/virtManager/asyncjob.py", line 108, in tmpcb
    callback(*args, **kwargs)
  File "/usr/share/virt-manager/virtManager/object/libvirtobject.py", line 57,
in newfn
    ret = fn(self, *args, **kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/share/virt-manager/virtManager/object/domain.py", line 1425, in
startup
    self._backend.create()
  File "/usr/lib64/python3.11/site-packages/libvirt.py", line 1373, in create
    raise libvirtError('virDomainCreate() failed')
libvirt.libvirtError: Unable to find 'memory' cgroups controller mount


And using command line:

# virsh -d 0 -c lxc:// start 101-PiHole
start: domain(optdata): 101-PiHole
start: found option <domain>: 101-PiHole
start: <domain> trying as domain NAME
error: Failed to start domain '101-PiHole'
error: internal error: Unable to find 'memory' cgroups controller mount

About the system:

# mount | grep cgroup
cgroup2 on /sys/fs/cgroup type cgroup2
(rw,nosuid,nodev,noexec,relatime,nsdelegate,memory_recursiveprot)

# uname -a
Linux 6.4.11-1-default #1 SMP PREEMPT_DYNAMIC Thu Aug 17 04:57:43 UTC 2023
(2a5b3f6) x86_64 x86_64 x86_64 GNU/Linux