Why can I watch only 2 episodes of The Morning Show during my 7 day free trial

Verify that you are signed in to the Apple TV app with the Apple ID account that has the subscription.

Sign in to the Apple TV app - Apple TV app user guide - Apple Support

When not signed in, you may find that you can only view a limited number of ‘teaser’ episodes.

Try updating the Roku Ultra box, if it has new firmware available or new version Roku OS available.

Try deleting and reinstalling the Apple TV app.