Resurrecting an old thread here...
I have a pair of Bose noise cancelling over-ear headphones which are not wireless.
So, for my iPad Pro M1, I got the Apple USB C to minijack adapter, and connect my headphones to that.
It works, i.e. sound gets transferred fine to the headphones...
But, the volume is out of control. After some minutes the volume will suddenly go to the max, and a few mins later it will lower the output by itself.. and go back to max again, etc. etc.
Very very annoying.. and reading this thread it might seem that making use of USB C to minijack just is not the way to go.