They're usually 1080p at most for the downloads, FYI. You can't download the 4K versions (at the moment anyway). At least, that was the case the last time I checked.
I believe you can download 4K versions, but the DRM-removing software I use, ViWizard, only works on an old version of iTunes. So for example I bought Trolls World Tour in 4K when it came out, but my DRM free copy is in 1080p because my app is old.