Another point is to help promote Spider-Man: Far From Home, the MCU movie that directly follows and is tied to Avengers: Endgame.
The cyclone monster (really the Earth Elemental) appears, and Mysterio tells Hill and Fury, “You don’t want any part of this,” and starts fighting the monster.
So the last thing added to the Avengers 4 bonus release is the opening scene to Far From Home.
The scene is set in a Mexican town that was devastated by a cyclone — except this cyclone seemed to have a face.