X11 forwarding with headless Ubuntu host

Dear group,

1. My workstation "gar" is running Debian 12 with XFCE.

2. I have another PC "marlin" running Ubuntu 24.04 LTS with XFCE.

3. I recently added a PC "octopus" running Ubuntu 26.04 LTS Server, 
without desktop environment.

4. Both "marlin" and "octopus" have a user "localadmin", on "gar" my 
username is "cgelinek".

5. I'd like to `ssh -Y localadmin@octopus` from "gar" and then start a 
podman container with `xeyes` in it and be able to see it on my screen 
on "gar".

6. I can do that with "marlin" (i.e. `ssh -Y localadmin@marlin`), but 
not with "octopus".

Some debugging suggests that when I `ssh -Y localadmin@octopus`, on octopus

  * $DISPLAY is localhost:10.0,
  * /home/localadmin/.Xauthority has the date of connection but
  * $XAUTHORITY is empty.
  * Unsurprisingly, when I try to run `xeyes` from within a container 
(with DISPLAY and XAUTHORITY being forwarded), it stops with `Error: 
Can't open display: localhost:10.0`.

I have checked that xauth is installed on octopus and have run out of 
ideas what to try next, any ideas?

Thanks for your time,
Christian