Originally scheduled for May 15, 2020 on PC, PS4, Xbox One and Stadia, Marvel's Avengers has been struggling to convince since its announcement during E3 2019. So it's not necessarily a bad thing that it's postponed to September 4th as announced by the co-leaders of Crystal Dynamics studio in this announcement.
It's time to use the few additional months to refine the game and try to make it an adventure that meets the expectations of fans of the franchise. Hopefully this will allow them to make a difference.