My snap version is the very same as yours, except my kernel has been updated to 5.4.65-1-pve. I tried the hack in the bug report, and it fixed it
ln -s /bin/true /usr/local/bin/udevadm
It forces udev to always return 0 so it is not a proper fix.
I do already have those in my config and my config only slightly differs in input and sound mount entry.
Here is my config
@PSteinberg, somehow my messages are deleted and some icons are disappearing here(totally unrelated). Anyway, HDMI output from LXC works on my laptop and i am able to run graphical app and control it with my keyboard and touchpad. However, the snap is not working, and it appears to be a bug(?)...