It could be another evil Strange, it could be the What If version, it could be a bait-and-switch. We assume there's an evil Strange because of the voiceover, but Mordo could easily be talking to Wanda. There's tons of leaks and trailers are supposed to misdirect you on some level.In the blue explosion from the trailer I could only see the guy had a ponytail so that must be this Defender Strange. Interesting that in back to back MCU movies they are really showcasing multiple variants of the main character. Cool to see one that is an evil variant.
Not sure if he is the one from What if...?, but would be some nice marketing for the What if...? show. He has black around the eyes in the show at the end, but doesn't talk evil-y like the trailer. He does however send those eldritch tendrils out of his hand in the trailer so I would like to assume yes, that is the same dark Strange. I hope this movie is as weird as I want it to be. Strange is in everything right now.
Edit: Watching some clips from What if...? again, I forgot how he was split in two then consumed the good side. While he redeemed himself and seemed normal, maybe the performance might be altered to keep him evil-y. But Strange was left in his universe so not sure how he would get to the one overlooking some place looking out into a universal swirl in the background from the trailer.
Defenders Strange remains a question, as I never saw him mentioned in any sort of leaks. So who knows what's the deal with him.
I can believe that a neurosurgeon would know less complex math than someone who's studying math/robotics/physics, that's just natural. But the way it was handled in that NWH was idiotic. It was like an early 10s "science **** yeah" type wrote it. Hell, with the way magic is presented in the MCU, you'd think the Sorcerer Supreme, with an actual photographic memory, would bother to learn some higher dimensional algebra. At the very least he would've gotten the hand of non-Euclidean geometry through sheer practice. But no, I guess web ropes shot on peaks confuse him too much.Dr Strange better be careful the villain in this film doesn't know math. Apparently math is his kryptonite.