First Problem that appears is that the Camera is stuck at Selfie-Cam and pressing the Maincam-Toggle-Button does nothing. It was updated to the newest Version of SailfishOS and this occures for the first time after some test-reboots.
Edit:
I could fix it with the search-function and this command:
dconf reset -f /apps/jolla-camera/
Thanks must go out to @attah wo did the mention here: