I didn’t particularly care for this episode.
I get that in this timeline Christine’s death was a “constant point in time” (Doctor Who apparently has the Trademark on “fixed point in time”). But it just doesn’t feel right that the entire story hinged on a unchangeable constant that was itself different from the “main” timeline. And it wasn’t just a single changepoint. There was apparently a significant changepoint well before the events of the episode, where Christine and Stephen fell deeply in love.
The Episode isn’t, “What If…Christine Died in the Car Accident?”, it’s, “What If…Stephen Strange And Christine Palmer Fell In Love (Way Before The Events Of His Movie), And Then Christine Died, And Her Death Were a Constant Point In Time, And Dr. Strange Tried To Change It?”