The tvOS 12.2 public beta can be obtained by going to the Settings app on the Apple TV and navigating to the Software Updates section under "System." "Get Public Beta Updates" will need to be toggled on, and once it is, the Apple TV will download the beta software.
tvOS 12.2, paired with iOS 12.2, lets users ask Siri to play specific media on an Apple TV from an iOS device. You can, for example, ask Siri to play Modern Family on the TV in the living room. This works for music and TV content.
No other new features were discovered in the tvOS 12.2 beta as of yet, and it's often difficult to determine what's new because Apple does not provide release notes letting us know what's changed.