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Or Spotify.

Proving that yet again Apple is held by a different standard to everyone else

They are going to add AirPlay 2 support once it is available:

(AFAIK AirPlay 1 requires dedicated hardware support.)

Google Play Music and Spotify both work with Sonos, without needing the awful Sonos app.

(I think you need the Sonos app installed, but, you don't need to use it)

Don't you need Spotify Premium?