Iron Man 4

Iron Man 4 was a planned sequel to 2013's Iron Man 3 and would have been an installment in the Marvel Cinematic Universe.

Plot
The plot is currently unknown.

Why It Was Cancelled

 * 1) Robert Downey Jr. expressed interest in making a fourth film and wanted Mel Gibson to direct and he was also interested but the project never prevailed.
 * 2) A War Machine spin off was also in the works but it too was cancelled.
 * 3) Tony Stark got killed off in Avengers: Endgame.

Results

 * The film was cancelled and the Iron Man films are now a trilogy.
 * A Disney+ series is in development that is tied to the Iron Man franchise, Ironheart. An Armor Wars series was also in development, but is now being retooled into a feature-length film.