Created attachment 110914 [details]
screenshot

After upgrading plasma, the brightness keys stopped working.

Turned out that the global shortcuts were not assigned any longer. (see attached screenshot).

So I clicked on "Predefinita" to resume them, and I got this error message:

"La scorciatoia «Monitor Brightness Up» è in conflitto con la seguente combinazione di tasti:
Scorciatoia «Monitor Brightness Up» nell'applicazione KDE Daemon per l'azione Aumenta luminosità dello schermo"

Which is about a conflict in the global shortcut. I clicked "reassign", and the error message appeared again, I clicked "reassign" again, and nothing happened, the shortcut did not get reassigned.

So I clicked on the button to assign the custom shortcut, and I pressed the screen brightness key. At that point, the selection automatically moved to "Predefinito", but this time it worked.

This thing happened on both my home and my work computer.