It's again rumored that a villain for Captain Marvel 2 might be Michael Korvac who is a cosmic heavy hitter in the comics (check out The Korvac Saga).
The latest rumor comes from the That HashTag Show where they offer up Korvac is a villain featured in the original Captain Marvel 2 script from Anna Boden, Ryan Fleck, and Nicole Perlman.
Worth a mention is that both Boden and Fleck got the boot following Captain Marvel failing, and the script has been rewritten by WandaVision's Megan McDonnell, so things regarding Korvac may have changed as Zawe Ashton is said to be playing the villain of Captain Marvel 2, thought to be the Skrull Queen Veranke or possibly Moonstone.
The site adds Captain Marvel 2 will feature multiple villains, with the story introducing a villain early on in the movie, the character Zawe Aston will portray, and the second will be a supporting character who is revealed to be a villain in the third act, which would be Korvac, and fits with the previous rumor (see below).
The site also thinks the recent casting call sheet featuring a "supporting male role" where Timothy Chalamet's name is crossed out with the role also compared to a Michael B. Jordan-type to be for Korvac, but I have my doubts on that as I think it's for a woke Nova.
I also don't think they would race-swap Korvac, as Korvac is a blond white dude in the comics who would make the perfect villain for Feige and Brie Larson's woke Captain Marvel 2 (recall "The Don" from the first movie).
Korvac rumors for Captain Marvel 2
Regarding the previous rumor about Korvac in Captain Marvel 2, and again which could be from a script that isn't being used, it's claimed Korvac will tie in with the Captain Marvel sequel and eventually will become a threat for the larger cosmic MCU.
The rumor offers Captain Marvel 2 will take place between Captain Marvel and Avengers: Endgame.
It's said the film will involve the Kree once again and the Skrulls and focus on their conflict. Carol learns of a "superweapon" and goes on a search for it, only to realize it's Korvac. She sympathizes with him, and she and Korvac bond over being guinea pigs for the Kree, basically; so when he betrays her and turns heel, Carol is left devastated.
Further details are said to include that they fight it out, with Carol actually trying to protect the Kree from Korvac, and he's defeated but scurries away.
Again, the Korvac storyline could be from the first Captain Marvel 2 script, but maybe Korvac will be used and go on to become a big Marvel Cosmic bad.