I wrote:
Until FC39, I had only run Wayland on one of my machines, not even trying to bring it up on the others. Since I intensely dislike the graphic login, I found a way to start it from a virtual terminal like I normally start X11. Instead of "startx", I have a short script I call "startw" that contains only the single line, "/usr/bin/dbus-run-session /usr/bin/startplasma-wayland". (Yes, I run KDE.) This worked on FC38.
Now on the same machine with FC39 (upgraded with system-upgrade) this no longer works. Instead, it produces 248 lines of output and then terminates. Reviewing those lines, it appears that it is complaining about, 'failed to open drm device at "/dev/dri/card0"' and 'No suitable DRM devices have been found'. I'm not sure what device that refers to but there seems to be some indication that it is my display. The display certainly works fine for the virtual terminal I use to run this script, and it also works fine for X11 if I run "startx".
Ok, so as a fallback I tried a graphic login. This reaches a completely blank screen and goes no further. The machine is up as I can reach it with SSH but the display is useless. It responds to Ctrl-Alt-Delete but nothing else. I can't get it to switch to a different desktop. I noticed that SDDM defaults to Wayland so I changed "sddm.conf" to include "DisplayServer=x11". The allowed the graphic login to reach a login page but nothing I entered there was accepted even when I switched to specify starting an X11 session instead of Wayland.
There are some online references to a problem with the /dev/dri/card0 device but they are ancient and don't seem relevant.
This machine is intended to run an application that only works on Wayland (Waydroid) so at this point I'm stimied. Any suggestions would be very helpful.
After much searching, checking alternate users, verifying permissions, etc, I determined I was unlikely to find the problem. I took the coward's way out and downgraded the machine to FC38. After that, the problem is gone!
I'll leave it at FC38 for a while while watching for any online comments that might provide a clue to a real solution.