Booting to black screen with mouse pointer after update

after applying via yast updates to packages, including kernel and nvidia packages, the boot finishes with a black screen on which only a mouse pointer can be ssen.

I can switch to a console via ALT-Ctrl-F1.
autologin to a user is set.
it’s a dual GPU. Both GPUs are shown in nvtop in a console.
if I execute systemctl restart xdm, the proper KDE/plasma desktop shows, but the next reboot gets stuck again with the black screen with mouse pointer

in case it’s relevant: dmesg shows:

[    8.944704] nvidia-modeset: WARNING: GPU:0: Unable to read EDID for display device DP-4
[    8.966266] nvidia 0000:01:00.0: [drm] Cannot find any crtc or sizes

How can I proceed for proper boot to KDE/plasma?
What information can I provide for error analysis?

deleting .cache solved it