Stormbreaker can be used by anyone, it isn't bound by Odin's enchantments to only be lifted by the worthy. Mjolnir is, however, still enchanted, meaning that only those that are worthy may wield it. This applies to your last two questions as well. If you can lift Mjolnir, you can wield it.
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.
Groot isn't worthy, he doesn't need to be worthy to pick up two unfinished parts of the weapon and join them. Stormbreaker is not blessed with odin's blessing it does not matter if he is worthy he can still pick it up. Anybody can lift it now kind of taking away the permanent leverage.
Film Theory: Is Thanos Worthy of Thor's Hammer? (Avengers Endgame)
Is Stormbreaker stronger than Mjolnir?
Powers and characteristics
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.
It's unlikely that he could give her Mjolnir, considering that so few people in the MCU have been deemed worthy of its power. So if she can't use Mjolnir, the next best option that's already in his possession would be Stormbreaker. He knows it can be an asset in battle, which is exactly why he would trust it...
It turns out the secret he was keeping about Tony Stark's parents – that Bucky (Sebastian Stan) was behind their deaths –was weighing on his mind, making him “not completely worthy” of wielding it.
Is Stormbreaker stronger than the Infinity Gauntlet?
Thor had the element of surprise and a weapon capable of overpowering even the Infinity Gauntlet. Stormbreaker powered through the gauntlet's energy beam but left Thanos alive long enough to succeed, making his victory in Avengers: Infinity War all the more devastating.
Mjolnir doesn't damage Cap's shield at all, as shown below. I think it is fairly safe to assume that Stormbreaker (being a cutting weapon, rather than Mjolnir which is designed to smash or build) would inflict similar damage to the shield as Thanos sword does. Conclusion: Stormbreaker minces Cap's shield.
If Marvel fans have ever wondered if Spider-Man was worthy of lifting Thor's hammer, the answer is yes. Just NOT the Spider-Man you think… Although he didn't really meet Thor beyond a couple shared scenes in Avenger's Endgame, Spider-Man has shown he's actually a big fan of the Thunder God.
There's a chance it could be repaired -- after all, Mjolnir has been broken and remade on multiple occasions -- but seeing Thor break Stormbreaker willingly is still a shocking sight. By destroying Stormbreaker, Thor not only reaffirms how powerful he is, but he also shows Bill how determined he is in his new quest.
Thor's hammer Mjolnir was defined by the fact that only the 'worthy' could lift it – so basically no-one except the god of thunder (and Vision, for some reason). But when it comes to the weapon's replacement, Stormbreaker – which Thor forges in Avengers: Infinity War – Groot is able to lift it too.
Originally Answered: Can Cap and Iron Man lift Stormbreaker now? Yes. Anyone can lift storm breaker. Because Odin did not said that Storm breaker can only be lifted by those who are worthy as he has said to Mjolnir.
MCU Thor cannot fly without Stormbreaker or Mjolnir. The best he can do is jump long distances, which is still dang impressive. Stormbreaker is called the King's weapon in Infinity War.
In the Marvel Cinematic Universe (MCU), the title of “weakest Avenger” is subjective and can vary based on individual perspectives. However, if we consider powers and abilities, Hawkeye (Clint Barton) often stands out as the least superpowered Avenger.
Odin is basically Thor and all the other Asgardians rolled into one—though he's even wiser, more experienced, and minus one eye. As the default King of Asgard, Odin is easily the most powerful being in his realm.
He has feats such as defeating Surtur (who can destroy a planet), conquering the 9 realms, and sealing away Hela. While there isn't much doubt that Thanos could beat Odin if he had all 6 stones, Odin could probably defeat Thanos if he only had one or two of them.
Thor. Thor, the god of Thunder, was undoubtedly the most powerful member of the original Avengers. His power continues to grow in the Marvel Cinematic Universe.
Aside from Thor being aware of Captain America's worthiness, the MCU set his amazing scene from Avengers: Endgame up throughout Steve's journey. The first installment featuring Steve, Captain America: The First Avenger solidified one of the main reasons why he was worthy of Mjolnir in the end: he was simply a good man.
Although Cap's internal conflicts prevented him from being fully worthy to lift Mjölnir during Age of Ultron, Cap really almost pulled off stealing Thor's thunder.
So, while Stormbreaker grows roots in Thor: Love and Thunder, it is not another Groot being grown but an extension of a plant with the feelings of a teenager. Stormbreaker's jealousy comes from being born of a teenage Groot, and that's why it's so anthropomorphized in the film.
Why does Thor love Mjolnir more than Stormbreaker?
However, it's possible that despite Thor's protests in the movie, he's always valued Mjolnir more than Stormbreaker. For all the power it possesses, Stormbreaker just can't compare to the long history that Thor has with Mjolnir, which has been by his side for several centuries.
The answer is that Thor can't beat Superman with his Stormbreaker, of course, his Stormbreaker will provide him extra power and capabilities but winning against Superman is not possible with that Axe. But it can harm Superman because the axe is enchanted and Superman is vulnerable to magic.
