I cannot get Plasma to start a Wayland session at all, despite looking through the Arch wiki, the nVidia 470 release notes, and the KDE wiki's article on the subject several times. Here's what I've gone through;
plasma-wayland-session installed: yes
egl-wayland installed: yes
output of "cat /sys/module/nvidia_drm/parameters/modeset": Y (so nVidia DRM is enabled and running)
Using Plasma 5.20.2 or later? Yes (5.22.3)
Using Qt5.15.0 or later?: Yes (5.15.2)
Despite all this, when I try to log into a Wayland session, I get a black screen for a moment, before it kicks me back out to the SDDM login screen again.
Modify /usr/share/sddm/scripts/wayland-session
At the end of the file replace the exec command with this:
exec dbus-launch $@
That didn't work, unfortunately. Same deal, black screen for a second before being booted back into the login screen.
You could try launching plasma without SDDM in the tty to see if nvidia+wayland is even working for you (no surprise if there's some kind of bug there).
XDG_SESSION_TYPE=wayland dbus-run-session startplasma-wayland
When I run that, this is the output I get:
Launching kwin
(kwin_wayland:3155): Gtk-WARNING **: 09:32:43.098: cannot open display:
KWin exited with code 1
startplasmacompositor: Shutting down
startplasmacompositor: Done.
Yeah so that would explain it. Kwin_wayland isn't even able to start for you. Your best bet is probably to consult upstream to see if this even works. I know allegedly plasma supports EGLStreams, but I have no idea about the stability and all that.
I actually had it running in KDE Neon, but switched to Artix both to get away from systemd, and to have more recent packages. Since Neon is based on Ubuntu 20.04, it doesn't even have the version of a few packages that nVidia requires with the 470 driver, one of which is notoriously hard to update in Ubuntu and derivatives (I forget which package).
Update: Finally managed to log into a Wayland session. However, a new problem has cropped up; anything that runs under Xwayland just shows a black window.