I have an issue where my Oppo A9 2020 starts the built in music app automatically when connecting to car bluetooth.  The Oppo site is quite clear on how to change this:

https://oppo.custhelp.com/app/answers/detail/a_id/9745/~/how-to-set%2F-change-my-default-music-player%3F

BUT this doesn't work as on my phone there is no music subsection under Default Apps. 

Anyone with an Oppo phone (I know a few around have them) know how to fix?  My google fu has failed me - other than to find a number of threads on other sites where people have similar problems but no solutions yet. I've tried all the obvious things like changing the music app in google settings, assistant settings, etc basically everywhere I can find to set it.

(The annoying thing is that this only started around the time I switched from Google Play to YT music - though I also got an upgrade to the Android version on the phone around the same time, so suspect one of those 2 things broke it.  I guess I could switch back to Google Play Music to see if that fixes it... but given they are discontinuing, it doesn't seem like a good long term option.)