Despite her great strength and heroism, ‘Captain Marvel’ isn't worthy enough to lift Thor's hammer in Marvel's ‘What If...?’. Having been called to deal with the rambunctious “God of Thunder” in this alternate timeline, Carol Danvers acted as Earth's cosmic bouncer, attempting to shut down the Party Prince before the chaos became too great. However, this led to a brawl between Party ‘Thor’ And ‘Captain Marvel’, and Carol found herself struggling to lift Mjolnir, potentially indicating that she's unworthy.
Despite ‘What If...?'s nature as an animated series showcasing alternate realities and timelines beyond the primary MCU, the rules of certain powers, characters, and items introduced should remain the same, such as Thor's hammer Mjolnir and its rules about its wielders needing to be worthy. In the primary MCU, the only wielders of the hammer beyond ‘Thor’ himself are ‘Captain America’ and ‘Vision’, as seen in ‘Avengers: Endgame’ and ‘Avengers: Age of Ultron’ respectively. That being said, this timeline features a Thor who never had a brother to challenge him, nor does it seem as though he was banished to Earth by his father Odin. As a result, this does create some confusion as to whether or not an enchantment of worthiness was placed on the hammer in this timeline.
Either way, it doesn't seem as though Captain Marvel is able to lift Thor's hammer, especially when he uses Mjolnir to pin her to the ground (a callback to the same move he used against Loki in the first Thor film). However, it's doubtful that she's simply not strong enough. ‘Captain Marvel’ certainly proves she's stronger than Mjolnir as she fights Thor thanks to her powers, implying that it's because she's unworthy while seemingly disproving actress Brie Larson's claims that Carol could lift the hammer. While this would indicate that Odin did indeed place an enchantment on his son's weapon, why would he do so if ‘Thor’ was never banished in this timeline? Furthermore, what is his definition for being worthy if Party Thor can lift the hammer just fine while Carol Danvers can't? —News Rush