https://wccftech.com/you-can-download-tvos-15-rc-for-apple-tv-4k-and-hd/

tvOS 15 RC is now available for download if you are a registered developer with Apple or a pubic beta tester.

While it may not be as exciting as iOS 15 and iPadOS 15, but tvOS 15 is a crucial part of the entire Apple ecosystem puzzle. It too received an update at WWDC 2021, several betas afterwards and now we have the RC build to play with.