SUMMARY After the upgrade to Plasma 5.16 the screen switch key on my Dell XPS 15 9570 stopped working. In previous versions it opened a dialog window where one could choose the output (on laptop screen, on external screen etc.). Now pressing it has no effect. It still emits Meta+P but it seems it is no longer bound to anything (I have not set up any custom shortcut but it used to work anyway with Plasma 5.15). SOFTWARE/OS VERSIONS Linux/KDE Plasma: Archlinux (available in About System) KDE Plasma Version: 5.16.3 KDE Frameworks Version: 5.59.0 Qt Version: 5.13.0 Kernel: 5.1.16
Still present in version 5.20.1.
I found the relevant shortcut in system settings under Shortcuts -> Shortcuts -> KDE daemon -> Switch display. There is a Meta+P default shortcut (and also a Display one which I don't understand and that has no contextual help) which was disabled; re-enabling it makes the display switch key do its job again. I'm sure I never touched it so it must have been toggled off automatically during the 5.15 -> 5.16 upgrade. Anyway my issue is solved.