As soon as the Infinity Stones were introduced in the Marvel Cinematic Universe, it became pretty clear that Marvel Studios was building towards some kind of adaptation of The Infinity War/Infinity Gauntlet storylines. This "Infinity Saga" culminated with Avengers: Endgame, but most of the studio's Phase 4 projects have been a little more standalone in nature, making it more difficult to predict where things might be going as we approach Phase 5.
The Multiverse has obviously been one major recurring element, and there's a lot of speculation that The MCU's next big event could be a take on Secret Wars. This does seem like a fairly safe bet given everything we've seen play out in the likes of Spider-Man: No Way Home, Loki and Doctor Strange in the Multiverse of Madness, but there are numerous other possibilities.
While speaking to Games Radar, Kevin Feige revealed that answers are coming soon (maybe even within the next few months), and said that there have been "many clues" already.
“As we’re nearing the end of Phase 4, I think people will start to see where this next saga is going. I think there have been many clues already, that are at least apparent to me, of where this whole saga is going. But we’ll be a little more direct about that in the coming months, to set a plan, so audiences who want to see the bigger picture can see a tiny, tiny, tiny bit more of the roadmap.”
Thor: Love and Thunder is next up in July, but we don't anticipate Taika Waititi's sequel dropping too many hints about what's to come. Promotion/marketing should kick in for Black Panther: Wakanda Forever by the end of the summer, though, so maybe that's what Feige is referring to? The rumored war between Wakanda's forces and Namor's people certainly sound like it could have some game-changing stakes.
Whatever this next big event turns out to be, you can bet Jonathan Majors' Kang the Conqueror will serve as the big bad (or one of 'em, at least), and we also expect the Fantastic Four to be involved in some capacity.