di you also try identifing "music player" as game, and then adjust gaming options?I have one feature request - disable sound on notifications when music is playing.
Right now I'm using MacroDroid which works, but there is an issue - if I turn on vibrate manually on slider, then play some music and stop it - MacroDroid automatically disables vibration even when slider is in vibrate position.
Okay, played with MacroDroid after posting this, managed to achieve this! Posting screenshot if someone wants to use the same approach
(not sure, could be a solution without esternal app)