SUMMARY
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STEPS TO REPRODUCE
1. Start Wayland session
2. Use display that automatically disconnects it output when no signal is detected
3. Leave system idle and wait 10 minutes for it to try to dim screens

OBSERVED RESULT

Screens turn off for a brief moment, but then immediately light up again. Process repeats every 10 minutes.
This is due to screen 'disconnecting' itself from graphics card output. On Windows you could hear 'device disconnected' sound when screen goes dark. There's no way do disable this behavior in Monitor menu.

EXPECTED RESULT

Screens should stay dark when there's no user input

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: openSUSE
(available in About System)
KDE Plasma Version: 5.27.8
KDE Frameworks Version: 5.110
Qt Version: 5.15.11

ADDITIONAL INFORMATION

The misbehaving monitor model is Lenovo ThinkVision T23i-20, but there should be others like this.