Apple has introduced all-new public betas for iOS 12 and tvOS 12. You must be a member of the Apple Beta Software program to receive the updates.
The new iOS 12 public beta 3 and tvOS 12 public beta 3 arrive nearly two weeks after the previous version and just days after similar developer betas were released.
Both iOS 12 and tvOS 12 should arrive for the general public this fall along with next-generation versions of macOS and watchOS.