The new Apple TV 4K is now available and Apple announced previously that they would be updating all existing HD content to 4K content on the Apple TV for free.
According to the guys over at MacRumors, the new 4K movies and TV shows are for streaming only, you will not be able to download the 4K content to your devices.
You can apparently download a local copy of a HD movie and also some movies which support HDR and Dolby Vision, but not 4K movies, you can see exactly what Apple has to say about this below.
You can download a local copy of an HD movie, and you might be able to download HDR and Dolby Vision versions, but you can’t download a 4K version.
As yet there are no details on why Apple has made it so you can only stream the 4K movies and not download them to your device.