BMW multimedia system does not connect with Bluetooth (only call audio)?

I have the following problem:

I bought a 2013 BMW 116d (VIN: WBA1C71040J947018). This has an on-board computer with a screen and the large navigation system / multimedia system.

Now I would like to connect my cell phone (Huawei P20) to this system to be able to listen to music via Bluetooth. However, this only works to a limited extent, because the list of connected devices on my cell phone only says "BMW 4207 call audio, contact release", there's no "Media audio" item. As a result, I can make calls and use the hands-free system, but I can't play music.

I have already installed the latest update for the on-board computer and my cell phone is also completely up to date.

Does anyone know the problem, or how do I get the "Media Audio" selection in the list of Bluetooth functions?

I would be very happy to receive helpful answers, thank you.

Had the same problem with a 2012 E-Class W212 and an iPhone.

At Mercedes it is due to a missing Bluetooth protocol.

I fixed it with a 13 euro adapter. Is plugged into a USB socket for power supply and at the back comes out a cable that is plugged into the AUX input. Goes wonderfully with the E-Class because both sockets are side by side in the center armrest and therefore no cables are visible.

Connect the phone to the adapter and radio to AUX and I was able to use the iPhone as a music source.

Only then can I no longer use my cell phone to make calls via the hands-free system, since the Bluetooth connection path is already blocked by the aux adapter. Then I have an audio output of the call through the boxes, but the cell phone microphone is being used and I can't answer the calls on the steering wheel, which is the point of not having to finger around on the phone while driving.

So my iPhone has 4 Bluetooth connections in the car.
Apple Watch
Multimedia system from Mercedes
Driving data dongle in the OBD box from Mercedes
AUX adapter