Apple is rolling out the fourth beta for iOS 12.3 and along with it, the public beta is also available to download. iOS beta builds are generally prioritized for registered developers (who do so for a fee) until the operating system is deemed stable enough for the general public to try out before its public release.
The fourth iOS 12.3 beta brings the new version of the Apple TV app, update with a new look and UI. With it, a new algorithm-based curator will suggest which movies and TV shows you should watch based on watch history and interests.
Image source: Mac Rumors