If you have a subscription, you can download the films for offline viewing within the app (usually limited to mobile devices): Max (formerly HBO Max)
Here's some information about downloading Harry Potter movies: Harry Potter All Films Download
The results flooded in—a digital Diagon Alley of shady storefronts. Some promised "High Speed 4K," others shouted "FREE" in garish neon fonts. Leo clicked a link that looked promisingly official, or at least less like a virus than the others. If you have a subscription, you can download
If you want to own the movies permanently without a recurring subscription, you can purchase "Digital Collections" from major retailers. These allow you to download the files to your authorized devices via the retailer's app. If you have a subscription