Since i believe Holy Knights work like Imu's Body (Similar to Nagato)
Buggy's DF basically Parallels Imu's Ability
It's possible that some Holy Knights will resemble each other (Just like Two Hands but One is Right & other is Left)
So Shanks was most probably supposed to be One of Holy Knights & this guy in Spoilers looks like him
I should remind Readers that Shanks was found on God's Valley as a Baby & despite this & fact He spent his Childhood on Oro Jackson, He revealed that He actually originates from West Blue (Where He says best Sake comes from)
This suggests that Imu is actually from West Blue or at least her Knights are chosen from there.
Now i shall remind you that not only Brook is a Former Knight but He is also from West Blue & his entire Sub-Story revolves around a Song called "Bink's Sake" which also originated from West Blue
Brook also said that his Signature Sword Attack comes from his Kingdom that is famous for it's Assault Squad (Basically Group of Knights).
And the Fact that He still introduces himself as a Knight & yet became a Pirate suggests that his Kingdom actually got Destroyed
(By none other than these Holy Knights, hence why Brook's Backstory is still reserved & He will be this Saga's Main Damsel In Distress)
Bink's Sake speaks about an Ancient Crew & i've said it long time ago that Shanks is a Descendant of this Crew's Captain, which just like Red-Hair Pirates & Straw Hat Pirates also had Nine Members, so Imu & Holy Knights's True Goal is related to that Crew's Story
That Crew's Story is similar to Noland, They found a Kingdom, exchanged Sake with it's Leader (Hence the repeated Sake Scenes) after a Legendary Fight & then They promised to meet again (Similar to Noland/Calgara, Yamato/Ace)
This is why Shanks appeared at End of Wano Arc just like Cricket appeared at End of Skypiea Arc (As Spectators), it's cuz just like Cricket is Noland's Descendant, Shanks is Descendant of Crew that once had a Legendary Fight similar to Luffy/Kaidou (Him loving to drink so much is another Reference)
But just like Noland, this Ancient Crew failed to find that Kingdom again, which is "Ancient Kingdom" (Currently inside World Snake in Elbaf).
So Shanks wants to fulfill his Ancestor's Promise (He thought Final Island is Ancient Kingdom, which is the Secret Question he asked Roger during Oden's Flashback, but after Roger said it's not, Shanks cried & decided to not go after One Piece, cuz He needs to look elsewhere, but He finally confirmed it's Existence in Kingdom of Elbaf, hence why He went there)
As for what that Ancient Crew had & needed to deliver, it was found by none other than Captain John which eventually became known as Captain John's Legendary Treasure, which He refused to share with his Crew which led to his Death, cuz He understood it's Value as something that's part of a Promise (Similar to Luffy's Straw Hat or Brook's Afro or Golden Bell)
So while Shanks was looking for Ancient Kingdom, Buggy was looking for Captain John's Treasure, cuz without realizing, They complete each other & They will be Key Characters in Final Saga in Elbaf