Comment # 6 on bug 1225296 from Takashi Iwai

First off, please verify that the problem persists with X11 modesetting driver
without X11 nouveau driver as suggested in the above.  If yes, install the Leap
15.5 kernel on your Leap 15.6 system with zypper install --oldpackage option,
reboot with it and check whether it still works as expected.

If Leap 15.5 kernel is confirmed to work, please boot with drm.debug=0x1e
log_buf_len=1M options, get dmesg output after the boot.  Take the logs from
both Leap 15.5 and Leap 15.6 kernels for comparison, and upload to Bugzilla.