It is confirmed that one doesn't have to be worthy to pick up Stormbreaker (which is how Groot managed to lift the head of the axe the stick). Having proved his worthiness by holding Mjolnir, we know Cap had the power of Thor coursing through his veins throughout that battle.
There also appears to be some mental strength required too based on the end of Thor's warning, so that part of Steve didn't come from a bottle. The other aspect of Captain America that could explain his ability to hold Stormbreaker is that he also previously held Mjolnir.
This is a very simple answer that a lot of people don't understand: You don't need to be worthy to lift Stormbreaker! Unlike Mjolnir, Stormbreaker was never enchanted by the forefathers to only be held by the “worthy”. It was simply a powerfully forged weapon with near-indestructible properties.
Many viewers have pointed out that Thanos was able to lift Stormbreaker without a problem, but this is because the ax isn't enchanted as Mjolnir is. Others believe Thanos lifted Mjolnir (although briefly) and have even argued that he would be worthy of doing so.
Stormbreaker has the additional power to summon the Bifröst, allowing Thor to teleport anywhere in the Nine Realms. Screen Rant has identified Stormbreaker as the more powerful of the two, based on this ability, as well as it being a much larger and edged weapon.
Unlike Mjølnir, however, the weapon is not enchanted to prevent those deemed "unworthy" from holding it, making anybody with sufficient strength capable of using the weapon.
This is a very simple answer that a lot of people don't understand: You don't need to be worthy to lift Stormbreaker! Unlike Mjolnir, Stormbreaker was never enchanted by the forefathers to only be held by the “worthy”. It was simply a powerfully forged weapon with near-indestructible properties.
It's important to note that the rules around worthiness had been temporarily suspended to allow this to happen. As soon as the fight was over, Superman couldn't lift the hammer anymore. However, under normal circumstances, without any weird interference, Superman is worthy of Mjolnir.
However, when Captain America attempts to lift it, it moves slightly, showing concern on Thor's face. If the Russo Brothers' thoughts are correct, Cap was really just showing humility and spared Thor's ego by not fully lifting the hammer.
Mjolnir has been manipulated in different ways in Marvel Comics, and many years ago, Iron Man was able to hold the hammer… thanks to zero gravity, meaning that he didn't properly lift it and he would have still not been able to wield it on Earth because he wasn't worthy.
Mjolnir has the enchantment where only those who are worthy can wield it, such as Thor or Captain America. Hulk on the other hand, … while Stormbreaker can be wielded by anyone who has the strength to do so (though it can be summoned by those worthy of Mjolnir like Cap did). Case in point, Thanos.
As Cap, Thor and Iron Man attack Thanos amidst the destroyed debris of their Avengers base, Rogers is suddenly able to summon and utilize Mjolnir, including the lightning power that it channels.
If Thor decides to use the power of lightning onboard the Asgardian refugee ship to fight the villain and his minions, he may accidentally damage the ship, or worse, even kill his own people. So, he chose to hold himself back, allowing some Asgardians to escape with Valkyrie (Tessa Thompson) and Korg (Taika Waititi).
Why did Stormbreaker overpower the Infinity Gauntlet?
Infinity gauntlet and stormbreaker are made out of the same metal, same forge. That is why stormbreaker was able to sustain those beams coming out of the gauntlet.
Actually everyone can lift Stormbreaker. Odin's enchantment was only for Mjolnir not for any other weapon which he would use in future. That is why Thanos was able to lift Stormbreaker and he was not worthy of Mjolnir.
Because it could kill thanos, is more powerful and thor panicked. Had he thought to call Mjolnir thanks would have gone to catch it and it would have knocked thanos on his bottom or something similar. But because thor was reliant on stormbreaker because it was more powerful he did it without thinking.
Mjolnir is not particularly heavy, it weighs 42.3 lbs. The fact that almost no one except Thor can lift the hammer has nothing to do with it's physical weight. The hammer is enchanted so that only those deemed 'worthy' are able to wield it.
Why does Thor like Mjolnir more than Stormbreaker?
It may be weaker than Stormbreaker in the Marvel Cinematic Universe's lore, but Mjolnir carries the bigger legacy since it holds a deeper meaning to Thor and anyone was worthy enough to wield its power.
Not Mjolnir. He is likely unworthy, so he would not have been able to lift up Mjolnir by himself. However, he did grab Stormbreaker, which DOES NOT have a worthiness enchantment.
