I’ve been poking around that corner of the fandom for a while. A really common one is the Ancient One's successor trope, where the reader character gets tapped as the next Sorcerer Supreme after Stephen. It sets up this intense dynamic of mentorship turning into rivalry, or sometimes a grudging partnership. I see a lot of fics where the reader has a unique, unstable magical ability that Stephen has to help contain, which becomes a vehicle for forced proximity.
Another massive one is the time loop scenario, obviously playing off the movie's premise. But instead of Dormammu, it's often Stephen trapped in a loop with the reader until some emotional confession happens. Honestly, it can feel repetitive if the payoff isn't earned. The hurt/comfort variant with Stephen's damaged hands is still everywhere, though it's less about the physical pain now and more about him learning to accept help.
I think the most interesting trend lately is fics where the reader is a creature from another dimension, or an artifact's guardian, giving the magic a stranger, less human-centric flavor. The tropes are familiar but the texture changes.