Currently external monitor birghtness is not handled. This is a feature request to add software support for external monitors brightness via MCCS. An example program that already does this/might be a good "underpinning" with more information on the spec/communication is ddcutil (https://www.ddcutil.com/). As an example, I can use the following ddcutil commands to set both monitor's brightness to 100%: $> sudo ddcutil setvcp -d 1 10 100 $> sudo ddcutil setvcp -d 2 10 100 Or 50%: $> sudo ddcutil setvcp -d 1 10 50 $> sudo ddcutil setvcp -d 2 10 50 As some extra background as for "why" my office has a lot of light in the morning/when it's snowy outside vs very dark at night, so I regularly need to adjust monitor brightness throughout the day. It's much more convient to do that with software. I think adding keyboard controlled/GUI slider based brightness integration would be a really nice feature for KDE to have for external monitors. It would be ideal to eventually be able to have some presets, maybe have a "default brightness curve" for the day, etc. However, the first step with any of that would be IMO, exposing basic brightness controls for the monitors.
We have DDCUtil support in PowerDevil: https://invent.kde.org/plasma/powerdevil/-/blob/master/daemon/backends/upower/ddcutilbrightness.cpp
Well I'll be, I rebooted just to see, but I still don't have any monitor brightness controls I can see anywhere. Perhaps Fedora isn't building their package with WITH_DDCUTIL. I've been using Fedora since roughly when it looks like this was implemented. I'll take that up with them... Thanks for implementing it, my bad :)