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 remember in the early post-Avengers days there was the theory that Clark Gregg was going to return to the MCU as Vision, and Vision was going to be based on Coulson’s brainwaves. Obviously this was before Agents of Shield.
Well, I’d count that as “halfway true”. Coulson returned in basically every kind of forms except as Vision lol