Plasma 5. The title pretty much says it. I can’t adjust the screen brightness anymore because the setting for it in the control panel has disappeared. The resolution/refresh rate and the compositor settings are still there.
https://bugs.kde.org/show_bug.cgi?id=398890 (Add monitor brightness to system settings)
That’s strange because I have always had a setting for that in Kde\Plasma until a few days ago.
I’ve no brightness setting under either “Display and Monitor” or “Power Management” on both current TW and Leap 15.0 (Plasma 5.12.6, Frameworks 5.45.0, and Qt 5.9.6) machines. They are, however, all desktop PCs.
The author of the bug report I linked to did say …
Right now there is no easy way to change monitor brightness in some configurations. While power plasmoid sometimes provides a brightness slider (happens in case of laptops), in other cases it doesn’t for no clear reason.
… note the “in some configurations”
Perhaps it may be beneficial if you could contribute to the bug report with details of how it affects your system. Maybe the hardware detection (which I’m guessing it could be based upon), has recently changed in some way, or has inadvertently became broken.