Simple, Egghead Arc answered this
When the man who beat Kaido & Co. entered They found Holograms, They are basically just an Illusion
But Atlas Gloves allowed her to Interact with them
Then We hear these words "Perception shapes your Sense of Reality"
Followed by: "Debates on what makes something Real is as old as time, it's something you'll have to decide for yourself"
World of One Piece is actually Normal Human World, Everything that makes it a Fantasy is "Not Real"
But Someone was able to see beyond this Physical World, They see their "Dreams", He is basically Oda but InVerse
They see everything as an Exaggerated Version of Reality
This was Foreshadowed by Usopp The Liar, He grew up wanting to see things for more than what They are & He shared his Vision with Three Others creating "Usopp Pirates", He sees a Dog but imagine it as a Cereberus, He sees a Lizard & imagine it as a Dragon, and He had countless Stories to tell, that's because Usopp is a Foreshadowing of "The Narrator" himself
So this Original Character represented Oda himself, represented Biggest Dreamer in the World, and just like Usopp who wanted his Lies to make others Happy, which is also what Oda is trying to do by drawing this "Imaginary" Story, that Character also wanted his Dreams to make entire World "Joyful" (Joy Boy...)
This Character eventually discovered something that allowed him to change the World in his desired vision, something that the World is gonna show you if you're truly the one who cares for it the most (Biggest Love towards the World)
Since Usopp's entire Character is a Foreshadowing of this Lore, then what did Usopp discover that his Crew (SHs) failed to see until it was too late? It's Going Merry's Spirit or what's called Klabautermann, it's the embodiment of Going Merry's Will & even though it's capable of moving Going Merry on it's own, it preferred to be moved by it's Crew
The same thing applies on the World itself, it's like a Ship & it needs it's Main Crew, and it's Will (Which represents Everything This World Has To Offer, literally Heart of The World) was only discovered by the Man who loved it the most & that's who i described above "Joy Boy", that's what One Piece is
And this Will of The World is basically Energy that runs it, if someone wields it They can re-shape the World in their desired way, Joy Boy can turn his Dreams into Reality, but just like only Usopp was able to see Klabautermann at first, only Joy Boy can see those Dreams take shape, They were basically just Holograms, People can't interact with Joy Boy's World, so what did Joy Boy do? He gave Haki to every Living Being!
Which is the equivalent of giving them the tools to interact with this New World based on his vision, just like from Atlas Perspective that Hologram City is Real & She can't interact with it thanks to her gloves, so Every Living Being became able to witness this Fantasy World we know of, it's like Haki is simply representation of Ink & Colors & Papers that Oda use which allow him to show us his Dreams (His Manga)
This was also foreshadowed by Miss Goldenweek who is only Character in One Piece who clearly have Inhuman Hax Powers & yet Oda confirmed She is not a DF User nor a different Race, it's like Oda trying to say that "Art, Colors, Drawing ... etc" are Magical even in real life, you don't need a DF to justify her Ability
So One Piece is just like Going Merry, just like that Ship represented SH's World that takes them to so many Fantastical Islands, One Piece Treasure needs a Crew & it will take them to countless Dreams, and this Treasure is only meant for the ones with "Biggest Heart", cuz Klabautermann only appear to those who take care of the Ship (Treat it like a Nakama, and not an Object)
But just like every Story, Joy Boy's Mission to make all dreams come true didn't come to fruition because just like Going Merry, One Piece wasn't strong enough, just like Going Merry was only able to travel Half-The World, OG Joy Boy's One Piece didn't last long, it did change the World into a Dreamy Place but it's an Incomplete Dream, what Roger Pirates found was basically Remains of OG One Piece Treasure that cannot be used, so the man who beat Kaido isn't gonna re-use Joy Boy's Treasure, He is supposed to Surpass him, the man who beat Kaido is gonna "Create" One Piece & it's gonna be more powerful than previous ones (Which is Equivalent of replacing Going Merry with Thousand Sunny)
And just like Franky said "Thousand Sunny can go anywhere, it represents a Ship that can journey forever, hence it's called Thousand Sunny", so the man who beat Kaido's One Piece is gonna have Infinite Potential unlike Joy Boy's OP which was Temporary, so the man who beat Kaido needs to find something that can Fuel One Piece Treasure forever!
What made Going Merry Fail? It was cuz the Crew didn't take care of it as much as Usopp, so Joy Boy's One Piece didn't last long cuz He didn't Unite the World, Haki used was "Temporary", now without telling this story in boring details, the Key to re-using One Piece Infinitely lies with Story's Main Villain, cuz just like every Story, there is always a Villain who ends up being the source of all world problems
Thankfully, Oda answered everything in Skypiea Arc, when it was revealed that just like Joy Boy Team, Moon People failed to keep Automata running due to lack of ressource (Electricity), so they went looking for a solution, but they eventually split into three groups (Different Paths), but the Person who led to Birkans, Skypieans & Shandians meeting again in One Battlefield is none other than Enel, Main Villain of that Arc, who also happens to have stole Goro Goro No Mi which was revealed to be the Infinite Resource that can keep Automata working!
So after One Piece World was created & then stopped evolving more, Joy Boy's Followers who wanted to find a solution eventually split into Three Groups (Three Kingdoms), and one of them found the Key to restoring One Piece & keep it running Infinitely, but unfortunately the Villain took it & just like Enel, He destroyed that Kingdom (It's none other than Land of Gods mentioned by Marco/WB)
What did this Final Villain of Story take from Land of Gods? Power that can fuel One Piece Forever, in other words "Infinite Haki"
Which made him secretly the God of One Piece World, cuz anything He does with his Haki, it has Unlimited Results (For example if He uses Hardening on a Weapon, it will remain Black forever, if He covers himself in a Barrier, it will remain forever ... etc)
But instead of doing these Haki Feats himself, He uses his Powers to empower certain individuals who are secretly this World's "Main Crew" and each of the man who beat Kaido's Crew Members must surpass a specific one of them in a particular "Role" (Not Combat, except Zoro)
Mihawk is just this God's Minion
Imu is just this God's Minion
Vegapunk is just this God's Minion
Blackbeard is just this God's Minion
... etc (There are Nine)
This God was revealed in Little Garden when Dorry said that their God knows of everything that is going on (Even if They are on complete other side of the World) and He has ability to give "Divine Protection/Judgment" to whoever He wishes to win, it's none other than "God of Elbaf" & He is Story's Final Villain, his Ability mentioned by Dorry is simply God of Elbaf coating his Haki anywhere in the world (And i'm pretty sure that All of the man who beat Kaido's Victories were his except Crocodile Fight where He was secretly buffed by God of Elbaf at the End, hence why Oda named that Finisher Gomu Gomu No Storm which is reference to D. will bring another Storm which is a word for Final Villain, just like Mihawk was Introduced in Chapter Titled "Storm", cuz He represented Zoro's "Storm" or God of Elbaf's Equivalent of Zoro, Mihawk)
I wanted to tell all of this Lore cuz it's necessary to understand how Haki shapes the World, so DFs follow the same exact principle but simply on a smaller scale, it allows to turn a Dream into reality & it's fueled by "Infinite Haki", however each DF is Exclusive to a single element (Either Natural Element or a Living Creature or different kind of Dreams we see in Paramecia Powers)
This is why DFs have those Swirling Patterns, cuz They use the same Energy as the World (Which Oda described in SBS), They are basically Devils who come from another Man-Made World (Imu's Secret Place) where They can use Haki to re-shape reality just like People once did in the distant past, how? By claiming their Souls, so those Devils gain the same functionalities as People once had, what People? Obviously ones who are related to Joy Boy's Original Groups (One of Three i mentioned above)
It's none other than Land of Gods, that's why Mary Geoise was created "After" Land of Gods was Destroyed, which means someone from Land of Gods survived & kept carrying the Memories/Experience of his Friends, it's literally someone who suffered same Backstory as Brook & became seen as The Devil himself who actually carries the will of more than one person (An entire Crew/Group)
So before DFs Existed, there is someone who originally turned into First Devil/Yokai & carried with him the Will of Others & eventually People started worshipping him as the Devil (Just like it happened with Brook after Kuma sent him away, One Piece have endless Foreshadowing everywhere), this Character gave birth to this Race of Yokai who not only inherited his Monstrous Form but also the Will of his People, until it was completely split into many Devils, each carrying a particular "Dream"
This Race is what eventually became DFs thanks to another Story (Which Mirrors Robin this time).
But regarding the First Yokai, there is someone who Inherited his Power, it's a Character who is based on a Pirate called "The Devil", someone who was referred to as "They", someone whose Body changed to match his Empowered Soul (Just like Brook), someone who embodies the source of all Devils, meaning He is basically their Home so He is immune to DF Restriction ... etc
It's none other than Blackbeard, meaning BB is Host of Last Survivor from Land of Gods & Father of All Yokai, and Mary Geoise represent Land of his Worshippers, meaning it's National Treasure is actually First Yokai's Treasure (Equivalent of Brook's Dial where his Friends Recording is Preserved), and Celestial Dragons used it to create DFs