Juli Clover, MacRumors:

With macOS Monterey, Apple has introduced expanded AirPlay 2 support, so you can ‌AirPlay‌ content from an iPhone, iPad, or even another Mac to your main Mac. We thought we’d do a quick demo of this handy new feature in our latest YouTube video.

The video is embedded below. Still thinking about use cases here. Throw some video from my iPhone onto my Mac? Whole house audio (mentioned toward the end of the video)? Note the mention of AirPlay’ed video being compressed to a lower quality.