In an interview with Business Insider, Avengers: Endgame directors, Anthony and Joe Russo, confirmed a speculation that fans had about Loki in the film.
Spoilers follow for Avengers: Endgame. Continue and your own risk and read our spoiler-free review of Endgame if you haven’t seen the film yet.
The Russo’s have confirmed that Loki did in fact create a divergent timeline after taking the Space Stone in the past timeline when Captain America and Iron Man went back to try and retrieve the stone.
Source: IGN.com Endgame Directors Confirm Loki Created a New Timeline