So did you read the post by Stevesky and look at the debug output? Wouldn't you agree that if it is passing AAC-LC as the audio format as it appears to be (and still was in late September on iOS 15) when using Airplay 2 it is irrelevant whether it is using ALAC for the actual Airplay stream itself?You and Naim forum users are confused.
Apple Music is managing the audio stream between Apple servers and your device. The stream quality is variable and displayed on the track selected. Not all devices can accept every format.
Airplay on the other hand is managing the audio stream between your device and amplifier or active speaker. It always use Apple lossless codec called ALAC and for music it is always at 16-bit 44.1kHz. These are explained on Apple developer documents and verified by 3rd parties.
Apple Music: See also Stevesky's post of June 9
Qobuz on iOS (ref. Stevesky's post of June 13)
See https://community.naimaudio.com/t/apple-music-hifi-tier-incoming/16445/699 for full posts
I like Apple Music and incidentally don't really give a hoot if it is passing AAC as I think it sounds great, just wanting to be accurate.
NAIM forum aside Apple Music's very detailed and carefully written support article which has been updated since May with the various additions such as Android and Homepod still doesn't mention Airplay as an official method of playing music losslessly.
Testing by others (Audiophilestyle forum) seems to show a bit perfect lossless stream over Airplay 1 however (in his scenario anyway).