The Russo Brothers set Avengers: Endgame up with a lot of references to the past. Some of the references are easy to pick up on, but others are so subtle that they fall into the Easter Egg category, like this newly discovered scene. As it turns out, the epic battle at the conclusion of the movie between Captain America and Thanos mirrors a scene from the first Avengers movie where Thor is fighting Hulk. When looked at simultaneously, one can easily see how much extra credit work went into making Endgame.
Speaking of extra credit, the Marvel Cinematic Universe fan who first noticed the new Endgame Easter Egg should get some. The fan goes by the name Thanos on social media, though we know it's not really the Mad Titan's official account (he's dead), and he figured out that the fight scene between Thanos and Captain America strongly follows the beats between the Hulk and Thor battle from the first movie. There's way too many similarities for it to be just a coincidence.
Mjolnir is the focus at the beginning of both clips and it flies into the hands of Cap and Thor at the same time as they go on to strike their foes. Both opponents get thrown back several feet and then throw back retaliation at the exact same time. The angles aren't the same, but the beats are nearly identical in spots. There's even a spot where Hulk and Thanos are both being choked out at the same time. Fans who are able to spot these Easter Eggs, especially between fighting scenes, are the ones who the Russo Brothers are looking to please with hidden treats like this.
Endgame hasn't even been out digitally for a full week and MCU fans are already finding a ton of Easter Eggs, though some are better than others. In another example of mirroring scenes from a previous movie, Endgame also has a scene that calls back to Captain America: The First Avenger. In said scene, Tony and Howard Stark are working in labs. Tony is assembling his Infinity Gauntlet and carefully placing the Infinity Stones using the same technology as Howard in the same manner and that scene is nearly identical.
Then there are the other Easter Eggs which become debatable between hardcore fans. One fan noticed that a girl in Peter Parker's high school towards the conclusion of Endgame is wearing a pink backpack, has blonde hair, and is wearing a spiderweb-printed skirt. Some will argue that it's a coincidence, while others believe it's a clever nod to Spider Woman, Gwen Stacy. For an Easter Egg like that, we'll have to wait and see if the Russo Brothers comment on it or not. However, the mirroring scenes is something everybody can see. You can check out the latest Endgame Easter Egg below, thanks to Thanos' Twitter account.