The newest addition to the Thor Franchise, Thor: Love and Thunder, featured a few powerful weapons in the MCU. Mjolnir was still a prominent weapon, but it was wielded by Jane Foster as Mighty Thor.
Mjolnir is Thor's signature weapon in both mythology and the MCU, but he has since grown accustomed to wielding the powerful Stormbreaker. While Thor's hammer is a powerful force, it isn't the most powerful weapon in the entire franchise. Over the course of the past 14 years, the MCU has introduced a variety of weapons that have proven to be great sources of power that outstep Mjolnir's capabilities.
Necrosword(s)
Mjolnir has changed hands a lot throughout the MCU, despite the concept that only those worthy of possessing the power of Thor can wield the mighty hammer. Hela was responsible for not only overpowering the hammer but destroying it.
However, she had her own powerful weapons. In Thor: Ragnarok, Hela was able to conjure different necro-blades, as well as her own powerful sword. Though Gorr the God Butcher's necrosword was inevitably destroyed by Mjolnir while Jane Foster wielded the hammer, this was after repeated blows from Zeus's thunderbolt.
Zeus's Thunderbolt
Zeus, the Greek god, was introduced in the newest Thor film, bringing more powerful gods into the MCU franchise. While fans are wondering if this god will make another appearance, his thunderbolt was the real star of the show.
Thor was able to defeat Zeus's power and take the thunderbolt to help defeat Gorr the God Butcher. The thunderbolt got a lot of screen time in Thor: Love and Thunder, and was strong enough to handle the fast battle with Gorr. Though it was used mainly as a hand-to-hand combat weapon, the thunderbolt in Greek mythology is considered the most powerful weapon on Earth and the Heavens, suggesting it could come into play later in the MCU.
Eye of Agamatto
It's hard to say who would come out victorious in a fight between Doctor Strange and Thor. However, The Eye of Agamotto has proven to be an extraordinarily powerful relic, giving its wielder powerful magical energy.
While the hammer is powerful in its own right, the Time Stone within the amulet has the ability to conjure time spells and alter reality. When combined with the other four infinity stones the power was unstoppable, but that's due to the fact of the extraordinary power of each individual stone. In a fight against Mjolnir, Strange could easily use infinite time loops to get the upper hand.
Stormbreaker
Stormbreaker is one of the most powerful weapons in the MCU, displaying extraordinary power not yet seen while Thor wielded Mjolnir. Gorr was able to use the power of the ax/hammer to open a portal to Eternity.
In Avengers: Infinity War, Thor has Eitri (Peter Dinklage), The King of Dwarves, forge him a new weapon to replace the then destroyed Mjolnir. When he appeared to battle Thanos' fleet at Wakanda, he was easily able to destroy Thanos' soldiers and the Chitauri fleet. Had Thor gone for the head, it could have easily ended the fight with the defeat of the powerful Titan.
Thanos' Dragonite Sword
Thanos is iconic for the use of the Infinity Gauntlet in Infinity War, but he had another powerful weapon before he was able to utilize the gauntlet. His powerful blade is featured more in Avengers: Endgame, able to withstand many blows from the Scarlet Witch.
His sword is made out of powerful Dragonite, an extraterrestrial stone used to forge weapons. Though he used something more powerful to destroy half of the world's population, he used this weapon while he was conquering and destroying worlds across the galaxy.
The Eternal Flame
The Eternal Flame is another weapon introduced in the Thor franchise. First seen in Thor: Ragnarok, the Eternal Flame is the source of Surtur's powers (and a fire giant that is iconic in Norse mythology).
The flame proved to have exceptional power, with Hela using its magic to resurrect her army of the dead and control Asgard. Later on in the film, the flame is used once again by Loki, who purposely brings Ragnarok down on Asgard to defeat his sister. While Mjolnir is a force, it doesn't have the energy that magical relics like the flame possess.
The Infinity Gauntlet
The Infinity Gauntlet is considered the strongest weapon in the MCU. Used to wield all five Infinity Stones, it has the power to do unspeakable things, like dust half of the world's population with one snap.
Eitri was also the forger of the Infinity Gauntlet, with Thanos tricking the King into believing his people would be safe if he created the weapon. The five Infinity Stones used within the gauntlet gave Thanos the power to do virtually anything he wanted. However, he was also able to use the power of the gauntlet to destroy the stones so no one else would be able to utilize the power.
The Nano Gauntlet
It's hard to say whether or not the Infinity Gauntlet or the Nano Gauntlet is more powerful. While Eitri is an extraordinary weapons smith, Tony Stark is also one of the best weapon experts in the MCU.
The Infinity Gauntlet was designed specifically to fit and be wielded by Thanos, but Tony (along with the help of Banner and Rocket) designed the Nano Gauntlet to adjust to the size of the user, making it a more versatile weapon. Both were used to utilize the power of all five Infinity Stones, though the Nano was used to restore the world's population.
Darkhold
This magical spellbook originally made its first appearance in Agents of S.H.I.E.L.D but was featured more in WandaVision. Crafted out of dark magic by a powerful god, the book contains dark spells. It also contains a prophecy about the nature of the Scarlet Witch.
The book was introduced to Wanda through Agatha, a dark witch that sought to manipulate the Scarlet Witch's power. After Wanda defeats Agatha, she attempts to use the book to find her sons in the Multiverse and played a major role in Doctor Strange in the Multiverse of Madness. Mjolnir is powerful, but it isn't capable of controlling magic of this magnitude.
The Ten Rings
The Ten Rings' origin is still somewhat of a mystery in the MCU, but it's understood that they're powerful extraterrestrial objects that give the wielder unbelievable strength.
Xu Wenwu utilized the rings to increase his longevity and used their powers to break out of the imprisoned Dweller-In-Darkness. His son, Shang-Chi, was able to use the power of the rings himself to defeat this legendary monster. While the Ten Rings are still quite new to the MCU, it's clear they have an immense amount of power.