How to install Apple's tvOS 15 public beta on your Apple TV
How to download and install the tvOS 15 public beta on your Apple TV With the Apple public beta program, you can download and install macOS Monterey on your Mac. Just make sure it's a secondary computer and not your main one, as it might be filled with bugs and could break things. To make things easy, we've detailed the download and installation steps below. Or, sign in if you’re an existing member. Accept Apple's terms and conditions. Once you’re signed in, navigate to the tvOS tab Scroll to the “Get Started” section of the tvOS beta page and enroll your Apple TV
Source: pocket-lint.com