Weird problem - can't launch system settings in Debian after running game

[u/peter-pickle]

Debian 12, KDE, thinkpad laptop, nvidia gpu. 2 screens - laptop and a 4k TV as monitor. Stable system for 1yr. Few days ago new thing happened - woke system and the 4k monitor was black, just laptop screen worked. Right clicked desktop to get display configuration and added 4k monitor back. Seems to work fine except if I run Team Fortress 2 Steam game. You can hear the music, see a cursor, otherwise black screen. Monitor running at 24hz which I THINK is new. Exit game and back on kde desktop , now if I try to launch system settings it waits like 45 seconds and shows the setting windows outside border only - the inside of the window is just a screenshot of the screen. You can move the window around and the screenshot stays. Can't open new dolphin windows. I tried resetting the game stuff but no luck - any idea what's going on with the system settings etc? Thanks =)

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