Some content may have an optional ‘Audio Descriptions’ (AD) audio track, which would include scene descriptions, like a narrator. Audio Descriptions is like a separate audio track, usually with “(AD)” behind the language name. It is also part of the Accessibility features on Apple devices and apps, where it can be set as default for new videos (if available in that stream). It is intended for the visually impaired users.
Use audio descriptions on Apple TV - Apple Support
Change subtitles or languages for videos in the Apple TV app - Apple Support
A few specific titles are intended to have a narrator, regardless of settings.
Please specify the movie title and the streaming service. A streaming service might have made an error, that can possibly be verified by other users.