Comment 25 for bug 1897224

Seeing as the issue was solved for two other people, I had another go - this time explicitly installing all mutter-related packages from -proposed (and not just 'mutter'):

$ aptitude upgrade libmutter-7-0 mutter mutter-common

Lo and behold, the socket showed up:

$ sudo ss -xlp | grep Xwayland
u_str LISTEN 0 1 @/tmp/.X11-unix/X0 60747 * 0 users:(("Xwayland",pid=2371,fd=4))
u_str LISTEN 0 1 @/tmp/.X11-unix/X1 60749 * 0 users:(("Xwayland",pid=2371,fd=7))
u_str LISTEN 0 1 /tmp/.X11-unix/X0 60748 * 0 users:(("Xwayland",pid=2371,fd=5))

and I can confirm that my graphical snaps all work again. I suspect that in my first try, not all packages were upgraded. I'm not sure, but perhaps that points at a dependency issue with the packages in -proposed.