Beta version

Channels Apple TV
#1

"To join the Channels DVR Beta beta, open the link on your iPhone, iPad, or Mac after you install TestFlight."

So, you can only get the beta version on the Apple TV 4K if you have an iPhone, iPad or Mac? I don't own any of those, but I do own an Apple TV.

#2

The Note on this page Channels — Beta Program tells you how

Note: The Apple Beta Program requires an iOS device to join through the Testflight app. If you only have an Apple TV, please email us.