While much of the film's plot remains a mystery, Marvel has released an official synopsis. The synopsis reads: "In Marvel Studios' 'Black Panther: Wakanda Forever,' Queen Ramonda (Angela Bassett), Shuri (Letitia Wright), M'Baku (Winston Duke), Okoye (Danai Gurira), and the Dora Milaje (including Florence Kasumba), fight to protect their nation from intervening world powers in the wake of King T'Challa's death. As the Wakandans strive to embrace their next chapter, the heroes must band together with the help of War Dog Nakia (Lupita Nyong'o) and Everett Ross (Martin Freeman) and forge a new path for the kingdom of Wakanda."
"Black Panther: Wakanda Forever" Villain
From the trailers, it looks like the comic book character Namor (Tenoch Huerta), the king of a hidden undersea nation of Talocan, will play the role of the villain. But Namor is more of an antihero than a straight villain, so it's definitely possible there's a bigger villain at work behind the scenes.
Image Source: Marvel Studios