Warning: SPOILERS for Doctor Strange in the Multiverse of Madness!
Vision's absence from Doctor Strange in the Multiverse of Madness was already secretly explained, all the way back during Phase 2 of the Marvel Cinematic Universe. Paul Bettany graduated from the voice of Jarvis to the synthezoid superhero Vision in Avengers: Age of Ultron, which included the tease of his relationship with Scarlet Witch (Elizabeth Olsen) that would define much of his future. After playing a major role in WandaVision, though, it was quite surprising to learn that Vision is missing from Doctor Strange 2 and the continuation of Wanda Maximoff's grief-stricken storyline.
Not only was Vision missing from Doctor Strange in the Multiverse of Madness, but he was barely even thought about during the movie. Scarlet Witch's mission is to be reunited with her children after the Westview anomaly ending took them away. Based on Wanda and Vision's past relationship as well as White Vision's existence in the MCU, it feels strange that she doesn't also look through the multiverse for another version of her husband. It seems that a life with Vision isn't even in consideration for Scarlet Witch after the Darkhold corrupts her, and the other universe she wants to live in during Doctor Strange 2's ending doesn't include her android husband.
There is actually a clear explanation for why Vision isn't with Wanda Maximoff in Earth-838 during Doctor Strange in the Multiverse of Madness, though. The majority of the movie's time in this universe is spent at the headquarters of The Illuminati. While this is where several surprise cameos come into play, Doctor Strange 2's Illuminati also includes good versions of Ultron bots. These Ultron bots are only used to escort Earth-616's Doctor Strange to the multiverse council and are easily destroyed by Scarlet Witch later on. However, their inclusion explains why Vision is missing in Doctor Strange 2. If the powerful AI doesn't turn evil like in Avengers: Age of Ultron during Phase 2, then Vision was never created in the Earth-838 reality.
Vision's MCU origin is directly tied to Ultron's plan for global domination. After upgrading his body to vibranium in Avengers: Age of Ultron, Ultron knows that there is still a higher form that he can reach and wants to develop a synthetic body made of vibranium and powered by the Mind Stone. This body is what becomes the foundation for Vision, whose matrix is a combination of Ultron, Jarvis, Tony Stark, and Bruce Banner - plus a power kick from Thor. Despite Avengers: Age of Ultron playing a prominent role in the MCU's storytelling, the good Ultron bots with Doctor Strange 2's Illuminati indicate that never happened on Earth-838.
Without Ultron's evil turn and Vision's creation, it is quite fascinating to consider the possibilities of how different Earth-838 is compared to the main MCU. Scarlet Witch wouldn't be traumatized by destroying the Mind Stone and killing Vision, while Quicksilver could also still be alive since Ultron was responsible for killing him. Doctor Strange in the Multiverse of Madness hints at a completely different fate for Wanda Maximoff in which she creates Billy and Tommy after settling down in less traumatic circumstances even without her partner, and it all stems from not meeting Vision or having to fight Ultron. The simple life with her kids makes it a bit easier to understand why she isn't seeking out Vision, even if he wouldn't be around in this universe.
