This Captain Marvel Endgame theory makes sense! As seen in the film’s mid-credits scene, Captain Marvel appears to support an Avengers: Endgame character theory. Carol Danvers’ arrival on Earth in Endgame’s post-credits scene prompted Nick Fury to summon her to help out in that battle. She wasn’t a massive part of Endgame, but Captain Marvel still had a significant impact on the battle against the Mad Titan and proved that she’s one of the most powerful characters in the Marvel Universe.
After the time jump, Carol returns to the Avengers: Endgame with a much shorter hairstyle than she had in Captain Marvel. No explanation for the change was given at the time (not that one was necessary).
When Captain Marvel appeared in her solo movie, her hairstyle was much shorter than it is now. Shang-Chi’s mid-credits scene shows that Captain Marvel’s hair has grown back out and is now much longer than before Endgame. Although it’s not explained, it does fit a popular fan theory about the Endgame.
It is revealed in WandaVision that Carol’s old friend Maria Rambeau died of cancer during the five years between Infinity War and Endgame. Captain Marvel’s hair in Endgame may have come from shaving her head to support Maria during cancer treatment, though there isn’t any evidence to back this up. It would fit Carol’s character and the close bond the two have shown. In Shang-Chi and the Legend of the Ten Rings’ credits scene, Captain Marvel has long hair again, suggesting that she shaved her head to support her friend and that it has now grown back out.
Carol’s hair has grown a lot in the six months since Avengers: Endgame. However, it isn’t quite as long as it was before the time jump. Perhaps Larson decided to change her hair length and then grow it back. Meanwhile, it would be more convenient for her to appear with her current hair length in real-life terms, especially for such a short scene in the movie. She went into space, was largely unaccounted for, and reappeared with much shorter hair in Shang-Chi’s credits, all of which fit the timeline of Maria’s cancer and death.
Given Captain Marvel’s new hairdo in Shang-Chi and the Legend of the Ten Rings’ mid-credits, it’s likely she’ll sport the same style in The Marvels as well. Since Carol and Monica Rambeau will be reunited in that film, it could – and arguably should – explain what happened. When Captain Marvel was mentioned in WandaVision, Monica didn’t appear happy about it; the Marvels can shed light on this. Carol showing she cut her hair in support of Maria could help demonstrate she was there for her friend when she needed it, taking a simple hairstyle change and making it a sentimental part of their adventures in the MCU.