The connection via Bluetooth was a Gefrickel. At some point it has then it works.
Unfortunately, only about 15 hours' drive. Then no connection was manufactured.
Ignition off. Removing device. Device reset. Other Bluetooth Devices ... nothing helped.
Frustrated as I was the unit got a slap ... Then the screen was broken and has shown nothing. Thus, the problem was also solved. The part wandered into the garbage and I found me a Sony.