What will Marvel do with the one original Avenger whose story is still a mystery?

Avengers: Endgame marked the end of the line of three of the original Avengers, including Black Widow, Iron Man, and Captain America. On top of that, two others expected to be retired in the near future, with the help of a new movie (Thor: Love and Thunder) or a TV series (Hawkeye). All of these characters will be replaced in one way or another, with MCU Phase 4 bringing the first new members to join an Avengers team that will face the next Thanos-like threat. But there's one hero left of the or...