SUMMARY
The battery applet in the System Tray cannot properly change the brightness anymore.
The "screen brightness" settings in "Energy Saving" are also not properly set either. As such, not putting this under System Tray.

STEPS TO REPRODUCE
1. Use the slider or the mouse wheel to change brightness
2. Brightness changes a bit but resets to a very low value (11%)
3. The actual slider value also gets reset afterwards
and
1. Set 100% brightness for "on ac power"
2. Plug the power cable
3. Screen brightness remains low

OBSERVED RESULT
Brightness level cannot be set using the tray icon anymore, nor enforced by Energy Savings settings.
Using `brightnessctl -d "intel_backlight" set N%` does change the brightness level correctly, and the slider in the applet will indeed correctly reflect the change. 

EXPECTED RESULT
Brightness gets suddenly reset to 11% instead of what the user specified.
This can also result in flickering.

SOFTWARE/OS VERSIONS
Operating System: KDE neon 5.25
KDE Plasma Version: 5.25.0
KDE Frameworks Version: 5.95.0
Qt Version: 5.15.4
Graphics Platform: X11

ADDITIONAL INFORMATION
All packages up to date as of 16-06-2022. Updates to 5.25 done using the offline method (restart).