Where do we draw the line?
Does an anthology approach like Playtime (1967, dir. Jacques Tati) count? It's got kind of an arc to it, but doesn't really have anything like a recognizable struggle with an antagonist. Unless you view brutalism as the antagonist, I guess.
8½ (1963, dir. Federico Fellini) could, likewise, be shoehorned into a discussion of the arc of the film--which it, itself deconstructs in the third scene or so. It's primarily a film about making the film. There's _kind of_ a journey the protagonist goes on, but does it really count as being this same plot?
Rashomon (1950, dir. Akira Kurosawa) is more of a multi-faceted mystery; we go through a progression of new information but no one really goes on a recognizable hero's journey--unless it's the listeners at the gate who are hearing the story.
Adaptation (2002, dir. by Spike Jonze) features Charlie Kaufman (played by Nicholas Cage) and his brother Donald (played by Nicholas Cage's twin brother) trying to struggle with this exact question of how to adapt a book that doesn't seem to conform to any usable pattern. I'm really not sure where it falls in this classification.