SUMMARY
***
If I select wayland, I can't log in. No surprise, given I have nVidia. However, if I select X11-
I can only use 2 monitors at a time. Any two. If I enable a 3rd, that monitor gets no signal and moving the mouse to the screen edge where that monitor is scrolls the entire desktop.
Attempting to set my main display to anything other than 1080 says "Using unsupported was possible in Plasma X11 session, but they were never guaranteed to work and   are not available in this Plasma Wayland session. "
I'm not running Wayland! 
***


STEPS TO REPRODUCE
1. Log in to Plasma X11 session
2. Enable a 3rd display.
3. Apply

OBSERVED RESULT
3rd display remains blank/sleep, desktop scrolls around if you attempt to move the pointer to where that third display should be

EXPECTED RESULT
All 3 displays on, with image, and ability to move pointer and windows to any of the 3 displays. 

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 5.26.4
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 5.101.0
Qt Version: 5.15.7

ADDITIONAL INFORMATION
This used to work fine and has been how I've used this computer since about 2018.