Brie Larson's Captain Marvel doesn't have a massive part to play in Avengers: Endgame, but the small role is an important one that required a lot of work when it comes to post-production digital effects.
However, it turns out it wasn't simply Carol Danvers' powers that required a lot of effects, but her costume as well. While Brie Larson wore a physical superhero suit on the set of Avengers: Endgame, it was decided later the suit needed to be changed up, and so a completely digital costume was drawn over Captain Marvel in post-production. According to visual effects supervisor Matt Aitken...
She was filmed with her physical costume with a great costume from the costume department. But after her sequences were filmed, it was decided by the filmmakers that her costume needed to be more different from the costume that she was wearing in the 25 years ago, whatever the era of the Captain Marvel movie. So we ended up replacing her costume with a CG suit for all her shots.
Brie Larson actually filmed Avengers: Endgame prior to making the Captain Marvel movie. It seems that one side effect of this was that only one suit was produced for the character. At the time, this probably made sense, but eventually it was decided that it Carol Danvers was going to change other things about her appearance in the 25 years of time that pass between the two films chronologically, she'd probably change her costume at some point as well.
Captain Marvel is one of the more interesting characters in the MCU right now simply by virtue of how new she is. Introduced in between the two recent Avengers film, and not having a massive role in the finale, we're still not sure quite where the character stands. The feeling is that Carol Danvers will be playing a major role in the future of the MCU, but we didn't really get that idea from Avengers: Endgame. She's clearly powerful, but that's about all we can say with certainty.
The fact that the character was introduced so recently, and then used so quickly, so much so that they clearly didn't consider how the chronology would impact the character's look, shows how Captain Marvel may still be something of an unknown quantity to Marvel Studios as well.
Or at the very least, she was at the time. While we don't know what the future holds for the MCU characters, Marvel certainly does. Bob Iger has said that we'll learn more about what Marvel has planned for the future this summer, and with both SDCC and D23 set to happen in the coming months, we can guess one or both of those events will be our massive unveiling.