Following the trailers for Captain Marvel and The Avengers: Endgame, it's revealed that Doctor Strange 2 is a go with Scott Derrickson returning as director.
THR offers a search for a writer is currently underway, and that Benedict Cumberbatch, Benedict Wong and Rachel McAdams will be back for the sequel. Derrickson did write the first movie's script, so it could be likely he will be working on the sequel as well.
It's further said the Doctor Strange 2 script should be finished in 2019, with the movie to start filming Spring 2020, for a May 2021 release date.
No plot details are obviously known, but Doctor Strange 2 is said to be a part of Marvel's "Phase Four," which is what Marvel Studios is referring to as their next batch of movies following The Avengers: Endgame (which caps the MCU Phase 1-3 films).
Last we saw of Doctor Strange was in The Avengers: Infinity War when he calculated only one possible winning outcome from out of the millions of future possibilities featuring the Avengers battling Thanos.
Strange also dropped the Avengers 4 title during Infinity War, when he told Tony Stark, "We're in the endgame now."
The Avengers: Endgame lands Apr. 26, 2019.