DeLub is right. The original Airplay 1 was device->receiver only. Airplay 2 has two modes, one which is device->receiver and one which is remote playlist oriented, like Spotify Connect. That latter mode is supported on Apple TV, Homepod, and a few third-party products like the Denon Airplay 2 receiver.
I don't blame people for being confused though. The public developer documentation for the latter feature is poor, and the interface is fairly inscrutable on iOS (but makes more sense on recent versions of iTunes).
Just to clarify,
@DeLub,
@ElNino, et al) I only have one ATV 4K which goes to a poor DAC built in an AVR. I have a good DAC but, it can only be used (remotely using Ye Olde Airplay 2.0) via an Airport Express via Toslink before going into the amp via analog. No HomePods.
However, as is usually the case, we are both, sort of, right and wrong. If we split hairs, Airplay has a connect like ability (since Apple did not brand it so, it is “like”) for ATV4K and HomePods and some other AVRs, apparently).
It seems Apple slipped in an update (making me, wrong as it concerns ATV and HomePods). I had not seen that new style remote icon ever before (when I last messed with this months ago as I have a life). Which seems to be a UI indicator of connectedness, perhaps, however, only via the main Airplay menu for the iOS device. Not via Apple Music.
or, it just opens the iOS remote. I forget what Spotify does but it is way more apparent when you are “connected”.
But, this is “connect” only to those Apple devices and, a few AVRs. Spotify Connect works across/plays from Spotify capable devices starting from a few years ago (For example, my expensive Pioneer AJ speakers were not updated for that or for Airplay 2 either… so I played Spotify only via Airplay to those). But anything new now has Spotify Connect and it is easy peasy. It is this, that I want, for Apple Music and iOS.
It is fine that ATV, HomePods, and new AVRs have this but, I want more and broader. Apple could make “connect” work from iOS to iOS with the snap of Cook's fingers.
Let us pray Airplay 3.0 clarifies it once and for all (I am joking).