This is on my laptop that's been running kde for 6 years, and I've tested plasma wayland before more-or-less successfully. But today attempting to login through sddm fails, just leaving me at the mostly black splash screen.
journalctl says this:
Jan 02 08:07:45 nbecker2 sddm[2890]: QProcess: Destroyed while process ("/usr/libexec/sddm-helper") is still running.
Jan 02 08:07:45 nbecker2 kded5[3986]: Failed to create wl_display (No such file or directory)
Jan 02 08:07:45 nbecker2 audit[3986]: ANOM_ABEND auid=1000 uid=1000 gid=1000 ses=2 subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 pid=3986 comm="
kded5" exe="/usr/bin/kded5" sig=6 res=1
Jan 02 08:07:45 nbecker2 kded5[3986]: qt.qpa.plugin: Could not load the Qt platform plugin "wayland" in "" even though it was found.
Jan 02 08:07:45 nbecker2 audit[1]: SERVICE_STOP pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='unit=sddm comm="systemd" exe
="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success'
Jan 02 08:07:45 nbecker2 audit[1]: SERVICE_STOP pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='unit=akmods comm="systemd" e
xe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success'
Jan 02 08:07:45 nbecker2 audit[1]: SERVICE_STOP pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='unit=plymouth-quit comm="sys
temd" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success'
Jan 02 08:07:45 nbecker2 kded5[3986]: This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may f
ix this problem.