if somebody says, there are already some posts with the same topic…
Yes there are but these posts couldn’t help me. Maybe because I am a god damn noob.
I tried cheese to check if my webcam is working and the app says, that there is no device.
So i tried some hints from other posts and also found out that the /dev/video0 cannot be open:
~ >>> v4l2-ctl --list-devices Cannot open device /dev/video0, exiting.
I hope you can help me!