Apparently, Sidious had no interest in the weapon because he left it behind when he took Maul captive. Mandalorian Prime Minister Almec, who orchestrated his escape from prison, informed the powerful Sith that some of his followers had recovered the Darksaber.
This implies that Palpatine had the right to claim the Darksaber for himself and rule Mandalore, though he inexplicably left the blade behind after he captured Maul. Once Maul was freed by his Mandalorian Shadow Collective warriors, they recovered the Darksaber and gave it back to him.
Because the Darksaber's sentience intertwined its fate with the rulers of Mandalore, Mando's rejection of that role meant that their wills could never align. That's why he has so much trouble wielding the weapon: it doesn't want to be wielded by a selfish bounty hunter who doesn't care about Mandalore.
The very first owner of the Darksaber was the man who created it, Tarre Vizsla. Very little is canonically known about Tarre Vizsla, other than the fact he lived during the Old Republic era and was, at that time, the only Mandalorian to have ever been accepted as a Jedi.
When he passes away, it gets passed down through inheritance to his son, Luke Skywalker. So technically. the Darksaber belongs to Luke Skywalker rightfully.
The black lightsaber, or Darksaber to give it its proper name, is one of the rarest lightsabers in Star Wars canon. Despite its rarity in canon, anyone who has seen the second season of The Mandalorian is likely to be familiar with the Darksaber.
According to the rules, Darksaber must be won by combat, which isn't how Bo-Katan received the sword. The Armorer doesn't recognize Bo-Katan as its owner since she didn't fight for it. That being said, Bo-Katan did try to earn it the correct way by going after Moff Gideon.
The Darksaber may be a fearsome weapon, but it cannot cut through beskar, which is the most resilient metal in the Star Wars universe and also Mandalorian-made. It is currently unknown if the Darksaber hilt is imbued with beskar, which would make it even more mighty in the eyes of the Mandalorians.
Ironically, the more Din Djarin uses the Darksaber the greater those issues likely become, because he knows this weapon should be used by the ruler of the Mandalorians - and he doesn't feel up to that task.
Sidious himself felt that he and his peers had outgrown the use of lightsabers, and only continued carrying them to mock the Jedi. He ultimately viewed his own lightsabers as little more than an affectation, and rarely wielded them in combat.
At the time of The Mandalorian story, it is pretty clear that Moff Gideon is not a Sith Lord even though he has the Darksaber in his possession nor does he have any links to the Jedi. Moff Gideon is nothing more than one of the Empire's existing bad guys who officially worked for the Imperial Security Bureau.
Eventually, though, Darth Maul stopped using the Darksaber. The most likely reason is that the Darksaber itself started disapproving of him as a master, thus becoming heavy and unwieldy.
Why didn't Palpatine use a lightsaber against Rey?
Palpatine's hatred of lightsabers actually explains both why he used one in the prequels, and mostly why he did not in Return of the Jedi. In broader Star Wars canon, it has been confirmed that Palpatine despises lightsabers, and sees them as a large contribution to the Jedi's dogmatic beliefs.
The reason there is only one is because the kyber crystal inside of the lightsaber took on the black color due to the contradiction of being both a Mandalorian and a Jedi at the same time, seeing as both groups hated each other (or in the Jedi's case, greatly disliked).
This was intentional and reflective of his general disdain for lightsabers; he believed that, unlike the Jedi, he was powerful enough not to require them, instead preferring a subtler approach to conflict, except when driven beyond all alternative to using them, as he was in Revenge of the Sith and a single episode of ...
After Sabine observed that the Darksaber is deceptively heavy, Kanan explained that energy follows through the blade, with the wielder directing its current of power. The wielder's thoughts and actions flow into the Darksaber to fuel this energy, affecting the weight.
All of that goes to show that Mando not being able to lift the Darksaber has nothing to do with how he acquired the blade or his failing the Creed. Accordingly, the best explanation is still that the Darksaber doesn't personally approve of Mando.
The purest form of beskar was capable of repelling the strikes of a lightsaber for brief amounts of time, and could withstand direct blaster fire. Pure beskar could still be damaged by weapons also made out of beskar; because of this, making weapons out of beskar was considered illegal by the Children of the Watch.
This is why we got a Darksaber and Mandalorian lore-focused episode inside The Book of Boba Fett. Boba Fett is present there as a Mythosaur part of the prophecy and the one who won't have any problems wielding the Darksaber.
How did Moff Gideon get the Darksaber from Sabine?
She was told by Moff Gideon that Mandalore would be spared if she commanded them to disarm. Despite weapons being a crucial aspect of the Mandalorian religion, she agreed, knowing it was the only way to save what remained of her people. In doing so, she yielded to Moff Gideon and gave away the Darksaber to him.
Din Djarin gave up the Darksaber so that Bo-Katan could rule Mandalore -- but not because he wasn't worthy of wielding it. Lightsabers are so deeply embedded in pop culture that even the most casual Star Wars fan knows the weapons' basics.
Cal Kestis' second lightsaber first appeared in the 2019 video game Star Wars Jedi: Fallen Order. Although the canon color of the weapon's blade is blue, its kyber crystal can be customized with the other possible colors of green, orange, purple, yellow, indigo, cyan, and magenta.
There is not a “rainbow” lightsaber, but there is a “white” lightsaber which could easily be all the colors of the spectrum. I ddi some research on this, and the current canon has most of the lightsabers either being green, blue, or like the Sith, red.
