Today, I eventually upgrading my F33 to F34. Everything looks fine
until I get teh sddm login screen. Here if I choose Plasma, either
Wayland or X11, I get a black screen with mouse, nothing else.
I found the issue. It was not related to Fedora nor KDE: I had a
locally compiled version of gcc in the PATH and after the update,
there was some missing libraries.
Sorry for the noise.