Warning! SPOILERS for Thor: Love and Thunder.
The MCU's rules for the multiverse have been notably inconsistent, but Thor: Love and Thunder introduces an even more vague concept in the form of Valhalla. The Infinity Saga only relied on a handful of fictional concepts such as superpowers, magic, and the Infinity Stones. They are all outlandish, but they're still clear enough to let viewers enjoy all of the MCU's first 23 installments to the fullest. Once the Infinity Saga ended, the MCU's Phase 4 took an ambitious step further with the debut of the multiverse and the afterlife.
The rules of the MCU multiverse are difficult to define. Loki established that the TVA eliminated all the people who threatened the Sacred Timeline. However, the Avengerswere inexplicably spared even though their Time Heist from Avengers: Endgame resulted in Loki's escape with the Tesseract, which in turn spelled the end of the TVA, the Sacred Timeline, and He Who Remains. Variants — who somehow can look identical or completely different from each other — can travel to other universes and go back home peacefully, like the many characters of Spider-Man: No Way Home. Soon after, Doctor Strange in the Multiverse of Madness explained that multiversal visitors cause catastrophic «incursion» events, even though Gamora, Steve Rogers, and Vulture apparently stayed in other universes without a problem. Steve Rogers, for that matter, shouldn't have been able to stay in the past and return to the present without passing through the Quantum Realm. There's also the fact that What If...? gave the Infinity Stones the power to affect the multiverse, even though they're supposed to work exclusively in their home universe.
Related: Wait, Did Thor: Love & Thunder
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