The last two episodes of What If…? Season 1 (read our What If...? season finale review) saw Ultron, or at least a variant thereof, return to the Marvel Cinematic Universe. Of course, the Avengers ...
I don't really theorize a lot, but I had this idea from reading a couple other theories. Back in The Avengers, Tony had JARVIS hack into SHIELD's mainframe and basically download all of their files.