Aside from adding support to HomeKit, Apple's tvOS platform adds a few small but useful features. Like iOS 14, it's getting picture-in-picture mode across the entire Apple TV experience, with AirPlay videos able to show up in picture-in-picture mode. Multiuser support is coming to the platform, but it seems only to be available for continuing gameplay on Apple Arcade games at the moment.
tvOS is also getting support for Microsoft's Elite 2 and Adaptive Xbox One controller, better audio sharing with AirPod earbuds, as well as up to 4K video streaming from your iOS devices' Photos app.
Source: The Verge