The monitor is not listed at all, so cannot be enabled"… I wish it were that simple.
I’m recalling the DP monitor display was glitchy/corrupted when I first booted it up (was off for vacation), but after I switched it to HDMI (my Steamdeck, which found and used it as expected without glitchy video) and then back to DP the display was no longer corrupted for the laptop… installed the updates, rebooted, and the display was absent… it may be possible the DP port on the monitor is borked and this was bad/coincidental timing.
I’ve discovered a new issue with SDDM. If I Super-L to lock the screen I’m left at a black/blank screen, SDDM is not presented to log back in.
The first time I encountered this, I did a REISUB… the second time I switched to TTY3 to see if I could find anything interesting in the journal (pretty quiet), and when I switched back to TTY2 SDDM was presenting.
Super-L again and SDDM was again not presented (blank screen). Switched to TTY1 then back to TTY2 and SDDM was showing.
So it seems to be that when I lock the screen, I have to switch away from TTY2, and SDDM will show when I return to TTY2.
EDIT: seems I’m not alone with the blank SDDM on lock… Plasma 6: Lock screen renders black (troubleshooting help) - Help - KDE Discuss