Probably not helping you but I am also experiencing the issue with my Mac Mini trying to Airplay with Apple TV. In my case, Mac Mini crashes and goes back to a log in menu. I brought my Mac Mini to the store but could not replicate. So I am suspecting my AppleTV side not being compatible, or some other interference perhaps my carrier's router or network now.

An update for my situation. I changed the name of AppleTV from Japanese to English then worked fine. https://discussions.apple.com/thread/252096898