I was able to make a little progress today. I locked the mesa packages and updated all the rest of my packages. After this was done SDDM worked, but Plasma still crashed when I tried to log into a Wayland session. When I switched to an X session that worked, and I am currently in an updated Plasma 6.0.3 session.
Unfortunately, Kitty is not behaving well after this update, frequently using 250% cpu, but if I switched to Konsole things seem to be running ok.