According to Deadline, who first broke the news of Evans' rumored return, Captain America 4 could be centered on Anthony Mackie's Sam Wilson, and Evans' reported return would be in a different project.
Of course, it's still very early days with Captain America 4, which was recently announced and has yet to be officially confirmed by Marvel. It's very likely the movie will feature Mackie's Sam as Captain America, though. Sam took up the mantle in The Falcon and the Winter Soldier's finale (to the internet's delight), and a title card at the end of the episode read "Captain America and the Winter Soldier." With that in mind, it seems unlikely Captain America 4 would pivot to something else entirely.
However, Evans poured water over rumors of his return, posting a tweet that read simply "News to me," complete with a shrugging emoji. Marvel Studios President Kevin Feige has also seemed to dismiss the rumor: "I rarely answer no to anything anymore because things are always surprising me with what happens, but that rumor, I think, was dispelled rather quickly by the man himself."
The Falcon and the Winter Soldier went out with a bang, with plenty of plot threads left tantalizingly unresolved: there's Sharon Carter apparently shaping up to be a new big bad in the MCU, while Countess Valentina Allegra de Fontaine, AKA Val, seems to be setting up an anti-superhero squad of her own.
Then there's also the question of whether The Falcon and the Winter Soldier season 2 will happen as well as the reported Captain America 4, or if the fourquel will incorporate whatever a potential season 2 might have been about. With Evans' rumored return also in the mix, there's plenty of Cap-related mysteries in the MCU to be resolved.