Wow. I didn't have such problems with KDE 5.26.5 and wayland.
(there were problems in games, with tearing, but that's not related)
I also observe this "gui freeze" of about 30 seconds with plasma-wayland session 5.27.2. I use proprietary Nvidia drivers (525.89.02). Steam is installed via flatpak. I'm happy to provide any further (technical) information if that would be of any help.
It also seems that it only happens for the first start of a cold-bootet system. Subsequent starts are fast.
Tried the beta again today and no longer reproducing on kde wayland 5.27.2, so closing.
Nothing extracted yet.
When opening steam on kde wayland, the client should be responsive on launch.
Steps for reproducing this issue:
Hardware information: https://gist.github.com/Bill5122/6694f883c71d24e9c8bd23dcf3cf0c32
Video attached.
https://user-images.githubusercontent.com/93512766/220536991-e2bf9f58-b490-4884-86aa-82ab2fe7447d.mp4