In 15 years of the MCU existing, I know that I have seen and read hundreds of different fan theories. There were some very popular ones, like Heimdall/the bofrost being tied to the Soul Stone, and some eccentric ones that only one guy insisted on but no one else believed.
What are your fan theory highlights?
I heard a theory that the reason why Loki made such an obviously fake oath of allegiance to Thanos only to be killed moments later was so that he could die “in battle,” go to Valhalla, and then return with an army of dead heroes in Endgame, possibly dealing with Hela in the afterlife.
Another theory: Thanos was going to use the Infinity Gauntlet to summon a villain from each prior appearance of an Infinity Stone who had been vanquished by the relevant stone. Red Skull was going to pop out of the space stone, Ultron out of the mind stone, Ronan out of the power stone, Kaecilius out of the time stone, Malekith out of the reality stone, and villain yet to be determined from the soul gem. Would have made for a cool anti-Avengers team.