It initially appeared that What If? might be a standalone series unrelated to the wider Marvel Cinematic Universe. However, if promo art for the show - not to mention the latest trailer - have confirmed anything, it's that these alternate versions of familiar faces will interact and possibly even unite as the "Guardians of the Multiverse."
Like Loki, the animated series will likely better familiarise us with the concept of the Multiverse, something that's bound to be further explored in Spider-Man: No Way Home and Doctor Strange in the Multiverse of Madness. Now, it also looks like What If? could introduce us to the big bad who is causing all these strange goings-on.
It's previously been reported that the monstrous Shuma Gorath sets his sights on Xochitl Gomez's America Chavez because he wants to use her powers to have complete control over the MCU's Multiverse. For those of you who don't recall, Chavez has the power to jump freely between realities, and for an all-powerful creature such as this, being able to make reality itself bend to his will by travelling from world to world would obviously make him an unstoppable force.
As you can see below, a possible first look at Shuma Gorath may have been revealed in the What If? trailer, and his attack could be what unites Captain Carter and this version of Doctor Strange.
It's hard to say for sure, but this series may be more important to the MCU than any of us realised...