https://comicbook.com/marvel/2019/04/09/avengers-endgame-fox-xmen-fantastic-four-cast/
Since the deal between Disney and Fox came to a close, fans have longed for information regarding the future for X-Men and Fantastic Four characters. Avengers: Endgame, however, finished production before the deal was accomplished and its directors are in no hurry to shove them into their ensemble film.
"It would not have been," Avengers: Endgame co-director Joe Russo told ComicBook.com when asked if it would have been possible to shoot something involving the characters. "That deal didn't actually officially close until a week and a half ago. It would not have been logistically possible."