In the “Loki” finale, Loki and his fellow variant, Sylvie (Sophia Di Martino), met He Who Remains in his Citadel at the End of Time. There, he explained how he keeps tabs on the final reality of the Multiverse. The three of them look at the timeline like a map and see exactly how events are transpiring. Then, He Who Remains drifts off as a rumble of thunder occurs, which visibly concerns him. He declares they’ve crossed the threshold now, and says he doesn’t know what’s going to happen. He could see the entire timeline at once up until this moment, but in an instant, something changed.
This change wasn’t caused by Loki and Sylvie, who were sitting in front of him. The ultimate tear in the multiverse wasn’t spurred by Sylvie killing He Who Remains, either, because he sensed this change beforehand. So is it possible that Wanda Maximoff (Elizabeth Olsen) transforming into the all-powerful Scarlet Witch in the “WandaVision” finale was the event that reopened the multiverse?