Now, if Thanos’ snap has happened, that would imply that no time travel has happened at that point of the film. After all, what would be the point in going back in time if not to prevent the events of the present? It’s possible this scene takes place before the team meets up with Scott Lang and learns of the Quantum Realm, and this is a mission half founded on stopping further destruction by Thanos, but mostly founded on revenge.
Article source: https://www.cinemablend.com/news/2469314/does-the-latest-avengers-endgame-trailer-reveal-when-the-thanos-rematch-will-happen