The two shots show his moustache looking significantly different from one to the other, shorter and darker in the first while the second shows more grey in and looks scruffier.
The gaffe is most likely due to Downey Jr. returning to set for reshoots and different shots being spliced together in the scene from separate filming sessions.
It was previously revealed the actor came back for last minute reshoots in January, months before Avengers: Endgame was released.
Iron Man’s final words, in fact, “I am Iron Man”, as he snaps his fingers was a last-minute addition to the movie.
source: express.co.uk