As described in this topic:
I am experiencing issues when logging in with the nvidia GPU as default.
The desktop would not show correctly. No access to panels or launchers.
Starting terminal (and programs through it) was possible as well as right clicking the desktop.
I wanted to share a work-around i just found:
Simply open the terminal and restart Plasma by:
kquitapp5 plasmashell and after that
Voilá, launcher and panels appear and everything works as expected.