Not sure if anyone has the same problem as mine, but I fixed mine on 2018 gmc sierra
My volume could go up to 30 ish in volume, when I put it louder it would go down in volume. Has done this to me twice in the last few years.
The way I’ve solved this problem is connect my Iphone to the stereo, open Apple car play, goto maps, pick a destination, when she talks turn up the volume, then it fixes your music volume. Not sure why they intertwine with each other sometimes, when they are supposed to be separate.
hope this helps someone.
