This is a pretty common BMW issue with M Performance brakes and there are endless posts about this. I, too, have the same unresolved squeaking issue. I bought my 2020 M550i used and had the stealership change the brake pads, etc. but still have squealing. There are many many threads about this and many frustrated BMW owners, not just for G30 series. However, not all BMW owners experience this which is even more puzzling. The only way I can temporarily resolve this is by power washing my wheels/brakes, but after 100 miles or so the squealing comes back. Some recommend going higher speeds and slamming on brakes, but that does not work for me. From the bottom F30 post, it appears that some have done a "deburring of edges" or chamfer on the brake pads. I have not tried this yet, but am inclined to do so once the weather gets nicer.
PUMA measure for the fix (#52226124-01). The service report states as follows: "REMOVED BRAKE PADS FROM ALL FOUR WHEELS USE A FILE TO CAREFULLY DEBURR THE EDGES ALL AROUND THE BRAKE PAD ON THE BEARING SURFACE FOR THE BRAKE DISC. CLEANED BRAKE PADS LUBRICATED BRAKE PADS. REINSTALLED AND TEST DROVE.
https://www.bimmerfest.com/threads/m...-stop.1443054/
https://f30.bimmerpost.com/forums/sh....php?t=1228900