Found the issue. I was initializing the AVAudioRecorder BEFORE switching the AVAudioSession category to .record. At least as of 16.2 beta 4, you now have to initialize it AFTER setting the record category. All fine with me, it's probably the recommended approach, but an error reason would be nice when .record() returns false, I'd been at this for 7 hours total before I finally got it.

Hello! Any chance you found a solution when playing Apple Music alongside an AVAudioPlayer?