Robert Downey Jr., playing as Tony Stark, once said everything about Chris Evans' Steve Rogers came out of a bottle. And, while that's not technically true, RDJ had a point. Still, the Super Soldier Serum exponentially increased all that Rogers was at that point in time, and ultimately, he became a pivotal member of the MCU's original Avengers squad as its leader.

Naturally, you'd expect his protege to take up the mantle, but that doesn't seem to be the case.
Anthony Mackie, the actor behind Sam Wilson, the former Falcon and the new Captain America, recently downplayed his character's ability to lead a team full of superpowered beings against threats from other planets and universes.
In an interview with Empire Magazine, Mckie shot down a popular fan theory that he'll serve as the Avengers' leader a few years from now, just like in the comic books, saying:
Sam is the only character without superpowers. He’s just a regular dude hanging out with a bunch of weirdos. Being from New Orleans, I’ve been in a few fights. And heart and charisma never helped me in a fight. That usually just got me beat up. So that might cause an issue when you go fight somebody like Thanos.
Of course, Mackie could just be staying true to his character. Humility is one of Captain America's key traits, whether it be as Sam Wilson or as Steve Rogers. So, it's very much like America's new behind to at least not volunteer himself as the new leader of the Avengers.
But, if it's true that the MCU will thrust someone else into a leadership role, it's not short of options.
In terms of seniority, Hulk, Hawkeye, and Thor, are leading candidates. Meanwhile, powerhouses such as Doctor Strange and Scarlet Witch are still around. Don't forget, rumors claim that Peter Parker will be the one to lead the Avengers in Kang Dynasty, and he certainly checks all the boxes. After his "with great powers come great responsibilities" moment in 2021's record-setting threequel, Parker is a lot wiser and more mature than someone of his age.
With that said, we'll have at least a few more years to speculate about who's going to lead the Avengers in Kang Dynasty as the film isn't expected to premiere until May 2, 2025.
In the meantime, fans can keep themselves entertained by checking out Ant-Man and the Wasp: Quantumania, which set a new series box office record despite negative reviews from critics.