Marvel Studios' The Fantastic Four isn't releasing until 2025, and yet there are already a handful of clues teasing its setting in an alternate universe. Despite being Marvel's First Family in the original comics, The Fantastic Four have yet to make their debut in the MCU, specifically its primary reality, Earth-616. To that end, an alternate universe could be the perfect answer to explain their absence.
https://screenrant.com/marvel-fantastic-four-alternate-universe-evidence/