You can learn a lot about Flee by looking at the three categories for which it has received an Oscar nomination: Best Documentary Feature, Best Animated Feature, and Best International Feature. It is the first movie in Oscar history to get nominated in all three of those categories, and it is clear from those nominations that this is not a straightforward presentation. Animation draws attention to its unreal nature, while documentaries at least pretend to show "real" life. By choosing to animate his film, Jonas Poher Rasmussen is making a statement about the veracity of documentaries.
The film is also complicated by the possible untrustworthy source of its narrative. Flee tells the story of the pseudonymous "Amin", who is a long-time friend of the director, and who is a refugee from Afghanistan. Rasmussen wants to tell Amin's story, wants to give Amin a chance to tell his story, but Amin has good reasons to hide behind anonymity. We don't know exactly what he looks like, since he is animated in a style so close to rotoscoping that we might forget the face is probably not a match for the real person. We learn of his escape from Afghanistan as a child, and to some extent, that explains all of the ways Amin hides the truth. Rasmussen assumes he knows much of the story, but over the course of the film, he learns that Amin has never told people his entire true story. The revelations are new not just to the audience, but also to the director.
Once you realize that Amin will adjust his story to protect himself, you question the validity of what he tells us about his life. The emotional makeup of the character feels very real, and his reasons for protecting himself are obvious. We sympathize with him ... we don't turn against him when we see how his story is sometimes a bit sideways to the facts, just as Rasmussen remains Amin's friend even as he learns that some of what he has known isn't literally true.
It strikes me that my two favorite movies so far from 2021 are documentaries. Summer of Soul remains my top choice, but Flee is in the same league.