Just a few updates based on the discussion in bug 1897224:
GNOME 3.38’s Wayland session included a behaviour change to stop listening on an abstract namespace socket for X11 connections:
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1424
This causes problems because the non-abstract X11 socket is not visible to snaps due to the sandbox’s private /tmp directory. We’re looking into it now, and the fix will either involve reverting the Mutter change (which would have to make it into your distro), or snapd would need to expose the non-abstract socket.
In the short term, the only workaround I can offer is to use the GNOME’s X11 session instead. I know that’s not ideal, but it’s all I’ve got to offer in the short term.