Warning: SPOILERS ahead for Spider-Man: Far From Home
Spider-Man: Far From Home has some major implications for the future of the Marvel Cinematic Universe - and among them is the first set-up for Doctor Strange 2. After Benedict Cumberbatch made his debut as the character in the 2016 solo movie, Stephen Strange went on to play a pivotal role in Avengers: Infinity War and Avengers: Endgame, using his powers to find the one possible future out of millions in which the Avengers could defeat Thanos.
Doctor Strange 2 hasn't been officially announced yet - but then again, neither have any other movies in Phase 4 of the MCU. Black Widow is already filming and other projects, like Shang-Chi and The Eternals, are known to be in development. However, given that Doctor Strange was a box office success, grossing $677 million worldwide, it's safe to assume that Marvel Studios will make a sequel in the not-too-distant future. After being "blipped" out of existence along with Spider-Man and trillions of other beings in the universe, Doctor Strange returned for the big final battle of Endgame and was joined by Wong and a small army of sorcerers. When the Elementals show up in Spider-Man: Far From Home, however, Strange is nowhere to be found.
Despite trying to leave his superhero life behind while he goes on vacation, Peter Parker is tracked down by Nick Fury during a school trip to Europe. Fury tells Peter that the world is under attack by extra-dimensional monsters called Elementals, who threaten to destroy the entire planet, and the only other superhero they have on the team is newcomer Mysterio. Desperate to avoid being drawn back into another world-saving conflict, Peter asks why the other Avengers can't help out (a common question/plot hole in the MCU's solo movies). Fury says that Thor is offworld and warns Peter against even invoking Captain Marvel's name. When Peter asks about Doctor Strange, however, Maria Hill mysteriously says that he's "unavailable."
Now, it could simply be the case that Doctor Strange, with his supernatural knowledge of the universe, knew that the Elementals were actually fake and posed no real danger to the planet. It's not unknown for the character to sit out of fights where he feels he shouldn't interfere, such as the Civil War arc in the comics, where he refused to take sides. However, the most obvious interpretation of Doctor Strange being "unavailable" is that he's busy with his own problems, which will be revealed in Doctor Strange 2. The movie probably won't be released until 2022 at the earliest, but since Far From Home is set in the year 2023, the two movies could take place simultaneously.
As for what those problems might be, the most likely villain for Doctor Strange 2 is Chiwetel Ejiofor's Baron Mordo. Though he and Strange were allied in the first movie, Mordo was disgusted by Doctor Strange's misuse of magic and ultimately turned away from him. Stealing back the magic that had been allowing a paraplegic man to walk around, Mordo ominously declared that Earth has "too many sorcerers." Perhaps in Doctor Strange 2, Mordo will somehow succeed in stripping Stephen Strange of his powers.
Spider-Man: Far From Home is our first real look at the impact of "The Blip" on an individual superhero franchise - though the biggest effect of the time jump on Peter's life was a younger kid having grown up into a handsome charmer who competes for MJ's affections. It will be interesting to see the fallout of Infinity War and Endgame on Doctor Strange's world - especially now that Stephen no longer has the Eye of Agamotto on hand to undo apocalyptic events.