I believe that's still supported by AirPlay. AirPlay 2 covers a bunch of related things working together, but the marquee feature was improved streaming syncs to support multiroom audio. I don't have access to an official spec, it's confidential, but there are portions that have been reverse engineered, and the core function is ultimately passing around an rtsp link. In some cases, that can be direct from a public source, in others it's a private stream initiated by the sending device.
The basics are functionally the same as Google or Sonos's implementations, in a heterogeneous house you won't really notice the difference. In an Apple household, you can do fun things like audio from almost anything, to almost anything. Apple TV to the speakers in the other room, iPhone to multiple rooms, a pair of HomePods paired to act as a left/right stereo, Apple TV to AirPods at night, etc.