After 2016's Captain America: Civil War introduced Wakanda and 2018's Black Panther delved deep into the hidden city's rich culture and traditions, Namor's entry to the MCU was all but certain. In the comic books, the Sub-Mariner has a long and bloody history of war against the vibranium-rich city as well as its protector, the Black Panther. At one point, the King of Atlantis flooded Wakanda. However, absent any official confirmation, we can't really say for sure if the MCU will head on over to the underwater city next. But, rumor has it, Marvel Studios will introduce the anti-hero to the MCU in Black Panther: Wakanda Forever as its villain.

Charles Murphy of Murphy's Multiverse recently responded to a question about Namor's involvement in Black Panther 2 on Twitter. Murphy then responded by saying, "I mean, he's the primary antagonist, so..."
I mean he's the primary antagonist, so... https://t.co/73zLxiikHr
— Charles I Don't Know About Trailers Murphy (@_CharlesMurphy) April 9, 2022
Murphy's "confirmation" is just the latest in a long line of rumors and speculations saying that the Sub-Mariner is coming to the Marvel Cinematic Universe.
Talks of Namor's involvement in the Black Panther sequel first began in June 2021 when insiders suggested that Marvel Studios had cast Narcos: Mexico's Tenoch Huerta as Namor among other Atlanteans. Then, in late March, Huerta fueled the speculations by posting a photo of himself on social media that he was in Puerto Rico, the same location as the production of Black Panther 2 at the time.
With filming on Black Panther: Wakanda Forever having already wrapped up, such "details" like these were inevitable. However, Marvel Studios' official word on Black Panther 2 likely won't come until we're much closer to the movie's theatrical release on November 11. Until then, fans are better off focusing on the MCU's more immediate release slate, like Doctor Strange in the Multiverse of Madness on May 6 with Ms. Marvel as well as Thor: Love and Thunder following suit on June 8 and July 8, respectively.