DAB playing music
Android Auto is running and Google navigation is active
You want to stop the music from DAB but still have the nagivation turn by turn guidance on?
If that's the case then you just need to turn the volume down when DAB is playing. Then you will only adjust the media volume bar and navi volume will be unchanged. Keep in mind here that if the turn by turn guidance will be triggered while adjusting the media volume, it will automatically switch to navi volume and you will end up adjusting that instead.
All the cars have usually 4 audio "signals" for the infotainment:
So each one can be adjusted seperately.