you can tell macOS to use AAC using an Apple tool called "Bluetooth Explorer". Also, Macs equipped with a T2 chip default to using AAC even without the manual i

you can tell macOS to use AAC using an Apple tool called "Bluetooth Explorer". Also, Macs equipped with a T2 chip default to using AAC even without the manual intervention. You can check what codec is used by alt-clicking the bluetooth icon in your menu bar and hovering over your headphones. There will a an "Active Codec" entry that shows which one is used (during playback).