The fundamental similarity between narrative and documentary films lies in the goal of telling a story as well as the audience's experience.
The differences between the two, however, mainly lie in the telling of the story and the techniques used to achieve the film.
Very simply stated, Narrative filmmaking is a pre-scripted movie with actors.
Documentary filmmaking is capturing reality in some way with the script often written AFTER the shooting has begun.
With narrative, the story and script are crafted in the beginning and with documentary, the story (often) unfolds as it happens.
References:
https://www.desktop-documentaries.com/martin-scorsese.html
https://www.studiobinder.com/blog/what-is-narrative-film-definition/#:~:text=Documentary%20movies%20vs.-,Narrative%20movies,used%20to%20achieve%20the%20film.
