Apart from all of the wild rumors surrounding Spider-Man 3, it has been officially reported by reliable trades thus far that Doctor Strange will be swooping in to help Spider-Man, possibly against a new incarnation of Electro played, once again, by Jamie Foxx. In terms of speculation about why Doctor Strange would be in Spider-Man 3, the most popular theory introduces Peter to the multiverse.
Filming for Spider-Man 3 has already started, with Tom Holland and Jacob Batalon reacting excitingly to the script. This is likely due to Doctor Strange's involvement in Parker's life on the run now that his identity has been revealed to the world, and he has been framed as a murderer at the end of Spider-Man: Far From Home.
Fans could potentially determine the extent of Cumberbatch's role in the movie sooner than expected since the star is likely to arrive on set soon.
Donald McInnes, personal hairstylist and makeup artist to Benedict Cumberbatch, on his private Instagram account posted an image of a salon room in Atlanta, Georgia.
WHAT THIS MEANS
McInnes does not state outright why he is in Atlanta, Georgia, but the most obvious guess is that he is there for Benedict Cumberbatch and his role in Spider-Man 3. While it is exciting that Cumberbatch may already begin filming for his role in Spider-Man 3, that does not give fans any indication of how large his role in the movie will be.
Cumberbatch confirmed at the beginning of October that filming for Doctor Strange in the Multiverse of Madness would either begin that month or early November. It is more likely that Cumberbatch is in Atlanta, Georgia, to film all of his scenes for Spider-Man 3 before quickly moving on to film the Doctor Strange sequel. It could actually point to Strange's role in Spider-Man 3 not being too large if Cumberbatch will only be filming for, at minimum, two weeks.
Additionally, Cumberbatch could be there early so that Sony can excitedly show off Doctor Strange's footage being in Spider-Man 3 and him interacting with Peter Parker in promotion of the movie at ExpoCine this December.