Of all of the original Avengers in the Marvel Cinematic Universe, Hulk's post-Endgame trajectory is the most unknown. Many of his founding colleagues are off the table, with only Thor set to receive a new movie. So, where exactly does this leave the Hulk? As fans will recall, Hulk was last seen in the intelligent Professor Hulk persona, but also heavily damaged after using the Infinity Gauntlet following the events of Avengers: Endgame. This leaves him in a completely different status quo then where he started, though with no clear path forward.
With the MCU moving into new territory for Phase 4, and the lack of an upcoming Avengers movie, it's unclear where Hulk could show up. This is compounded further by the murky situation surrounding the Hulk film rights. Marvel has already announced most -- if not all of Phase 4 -- along with several new TV projects. These bring about several possibilities that could also bring the Hulk back in a supporting role.
Thor: Love and Thunder
While Hulk had a large role in Thor: Ragnarok, which loosely adapted the Planet Hulk storyline, it seems doubtful that he'll return for Thor: Love and Thunder. Especially given the film looks set to focus on Jane Foster's turn as Thor with the return of Natalie Portman. Still, with writer and director Taika Waititi, who also helmed Ragnarok, returning for Love and Thunder, there does appear to be potential to see Hulk again, as well. Other than a returning director, however, there's not much reason for Hulk to be in the next Thor.
Doctor Strange 2
The very premise of Doctor Strange and the Multiverse of Madness means that fans might see alternate versions of existing characters. The added horror angle makes the appearance of a monstrous Savage Hulk all the more appropriate. Having the Hulk as a sort of Lovecraftian monster would also restore the character's horrifying characterization, which has been heavily neutered with his more recent, comedic portrayals.
Strange and Banner -- along with other heroes -- also formed the team known as The Defenders. There has yet to be any setup for this team in the movies, though, so doing it now would be somewhat random. Although, it would give a team for Banner to be in besides The Avengers. Of course, as fans will note, The Defenders moniker has already been used in the MCU for the Netflix series characters. Given the MCU's reluctance to use the Netflix continuity, however, recycling the name might be possible.
MCU Solo Hulk Movie?
One reason that the Hulk has been defined by the Avengers movies is Disney not owning the film rights to produce a Hulk solo film. The Hulk movie rights are currently co-owned by Paramount, meaning Disney would have to distribute the potential movie through Paramount. Marvel's ambivalence, understandably, in making another solo Hulk movie comes from having to share profits with another studio. Marvel may want to fully acquire the Hulk rights, however, if only to prevent what happened with Spider-Man. The current situation with Marvel and Sony has been extremely controversial, especially coming after Marvel's acquisition of the Fox and in doing so gaining the rights to the X-Men and Fantastic Four.
Of course, Marvel may move to buy the rights completely from Paramount to get as many of their eggs back in their basket as possible. In doing so, Marvel could finally make another solo film to expand the character's mythology. Banner's villains and supporting cast have been largely ignored since 2008's The Incredible Hulk. This gives the character untapped potential that could be used in a new film. Given the Professor Hulk's use in Avengers: Endgame, a new Hulk movie could use further elements of the iconic Peter David Hulk run. But this all hinges on the character's movie rights being secured and, as of now, that seems doubtful.
She-Hulk TV Series
The recent announcement of the She-Hulk series on Disney+ creates probably the most obvious outlet for Banner's return. Jennifer Walters' origin in the comics involves a blood transfusion from her cousin Bruce Banner -- aka the Hulk. If the show is anything similar, it'll require Ruffalo's Banner in some capacity. Hulk may even already be in a hospital for the damage sustained in Endgame. A show wouldn't have the same rights issues as a movie, either. Thus, the show could also be used to reintroduce characters such as Betty Ross.
One potential problem with this would be the budget. Though a Disney backed show won't be cheap, a series with two green gamma people will require a heavy budget to look good. Endgame also left the character in the Professor Hulk role. Having the character unable to become Bruce Banner again makes the budget issues that much more apparent, especially if he has a substantial role.
It's worth noting that Ruffalo has one film left in his contract. That film could be any of those mentioned above or another yet unannounced MCU film. While an appearance in She-Hulk is more than likely all but confirmed, it's unknown where or what Hulk will smash after that.