No mouse after switching to KDE in 4.2-rc4

My computer is a desktop PC that was running Qubes since 2020.
I did a fresh install with 4.2-rc4 because the update to 4.1.2 broke my previous install (login screen seems dead)

After login I get prompted to allow the mouse. After confirming the mouse works fine.

After switching to KDE the prompt doesn’t appear anymore and the mouse stays dead.

Any suggestions how to fix this?