will dolby atmos be available through apple music without apple tv?

Sonos doesn’t release what they’re working on, with very rare exceptions, in advance, so it’s unlikely that you’ll be told. And since the majority of the chips built in to Sonos are effectively for stereo, it’s unlikely to be offered for regular speakers. 

I’ve never seen Sonos do a stream that is restricted to a single device, in this case the Arc, which is the only Sonos speaker that can handle 3.0.2, so I suspect that we’ll be restricted to using Apple TVs to send the signal to the TV set, and then HDMI ARC to send the signal to the Arc itself. 

https://techcrunch.com/2021/06/08/apple-music-launches-spatial-audio-and-lossless-audio-adds-spatial-audio-playlists/

“Apple is planning to bring the new Spatial Audio with Dolby Atmos feature to Android devices in the near future, according to a brief mention on the Spatial Audio intro page available in the Apple Music app.”

So that doesn't address whether or not it will ever be available directly through the Sonos app, but it does suggest it could be available to Android tvs “in the near future” via the Apple Music app.  And if that is the case, it should work with my Sony tv with my Sonos Arc surround setup (without having to own an Apple TV device).