tvOS 12.4 is a free update that can be downloaded over the air through the Settings app on the Apple TV by going to System > Software Update. Apple TV owners who have automatic software updates turned on will be upgraded to tvOS 12.4 automatically.
There were no new features discovered during the beta testing period for tvOS 12.4, making it unclear what's included in the update.
Apple does not provide release notes for tvOS updates, making it difficult to determine what might be new or improved in the operating system.
The update likely focuses on introducing performance improvements and bug fixes, and there could be some refinements to the TV app that was introduced in tvOS 12.3.
Apple has also released new 7.3.1 Apple TV software that's designed for the third-generation Apple TV.