In What If…? episode 7, “What If… Thor was an only child?” Thor’s hammer, Mjolnir, is prominently featured. However, the MCU forgot how the rules for the weapon’s “worthy” criteria function. This series is set in alternate timelines. Here, each episode is centred on a single change that has significantly different consequences in each of the alternate narratives. Aside from that one exception, the world’s rules are supposed to remain the same as they were in the MCU. Thus, what exactly is going on with Mjolnir is a mystery.
Loki has now returned to the Frost Giants at birth. What If…? episode 7 sees an uncontrolled and unchallenged Thor descend to Earth and cause mayhem with his wild partying. In response to the out-of-control party, SHIELD attempts to discover a means to stop Thor. Maria Hill enlists the assistance of Captain Marvel. The battle between Thor and Captain Marvel spans the globe. However, it comes to an end when Thor places Mjolnir on Captain Marvel’s stomach. This disables her from standing up.
What If…? makes use of the actuality that as is in the Marvel Cinematic Universe. In the MCU, only those who are worthy of Thor’s power are able to wield his hammer. Furthermore, this “worthiness” criterion has extremely strict rules. And only Thor, Steve Rogers, and Vision being able to wield the hammer at any given time. That rule, however, is only established when Thor is exiled to Earth by Odin in Thor, and the All-Father auras Thor’s hammer so that it can only be raised by the worthy.
This is a direct consequence of Loki’s interference, and it is clear that it did not occur in this timeline, as Thor has not learned the lessons he did in Thor but has never met Jane before this point. Captain Marvel ought to be able to more easily stand up and throw Mjolnir back at Thor if the hammer’s enchantment is removed.
If, for another purpose, Odin had set the same enchantment on Mjolnir in this What If…? timeline, that poses further concerns. While the manner that Odin defines worthiness is often dubious, for Party Thor to be declared worthy by the hammer but Carol Danvers to not seem implausible. Furthermore, if Party Thor were regarded worthy of lifting Mjolnir then it would devalue Captain America’s Avengers: Endgame usage of the hammer.
The MCU has played fast and loose that govern Mjolnir previously, but typically in manners that have at least some rationale. Significantly, in Thor: Ragnarok, Thor tosses Mjolnir towards Hela. Luckily enough, she catches it, wieldes it, and smashes it. One prominent theory to describe this is that Odin has died recently and with his passing, the enchantment has been undone. However, What if…? has no viable alternatives for this as Odin could be in the “Odin Sleep.” However, he is very much alive.