Earlier today people on Reddit and Twitter noticed something in 3D versions of the Avengers: Endgame trailer that were posted on YouTube. In the shot of Hawkeye running down the exploding corridor, bodies could be seen in the fire when they cannot be seen in the 2D version of the same trailer.
I managed to track down the source footage the YouTubers used to create the 3D trailer, and confirmed that you can indeed see the bodies in the fire. It’s only in the 3D version of the Avengers: Endgame trailer, they’ve been digitally removed in the 2D version. And yes, they are Thanos’ Outriders from Avengers: Infinity War, although they look like they have a slightly different head with what look like horns.
Here are comparison shots. 2D on the top and 3D on the bottom:
I guess this is your first concrete example of how Marvel has digitally altered their Avengers: Endgame trailers to hide plot elements.