I am trying to get guitarix with jack running on a Pi4. The USB Audio device is working properly for line out e.g. watching youtube.
As soon as I start jack and guitarix, the audio stops playing. Now I've set up Jack and guitarix like this:

But there is no sound input when clicking the Tuner Tab in Guitarix. I tried connecting a guitar, a microphone but no sound.
What could I've done wrong?

