It's stated on the Plex website - " * These apps cannot open another service app" and they list:
- Plex HTPC (v1.14.0 or newer) *
- Roku (v7.0.3 or newer) *
- Smart TV supported models (v5.34.1 or newer) *
On Apple TV it opens the episode / movie directly in Netflix etc when you click on it. My problem is that currently, you can't add Disney to the list of streaming services if you are in SA (but available in other countries). Maybe because Plex Discover still needs to be updated after Disney+ was launched in SA, or because of Disney's cellphone authentication. Either way, it would be convenient if Disney+ was also supported.