Is man the real mystery in "A Very Old Man With Enormous Wings"?
Here, it's not obvious whether you mean "man" in the sense of humanity as a whole or "the man" (with the article accidentally omitted) in reference to the old man with the wings.
"A Very Old Man with Enormous Wings" by Gabriel García Márquez is an example of a genre called "magical realism" in which fantastic elements are introduced into everyday life. The old man is such an element.
The old man, who speaks no known language, and eventually is able to fly with his giant wings, is in one sense a mystery. He is both fantastic and puzzling to the villagers. On the other hand, that isn't really the point of the story which is more focused on how the villagers respond to his presence. Although he makes Pelayo and his wife wealthy, they do not react with gratitude, and though the villagers initially suspect the man of having a potentially angelic nature, they eventually mistreat him in the way they would a circus freak rather than seeing him as something beautiful or wonderful. Thus rather than being a mystery about the man with the wings, the story is more about the mystery of the inhumane nature of humanity.