Shanks is probably the Yonko that has the least endgame goals of all the Yonko.
Shanks seems to be that person that is just having fun and partying with the people he likes and loves, while still desiring to be free and lawless. The fact that Shanks is such a laidback guy that isn’t actively pursuing more power, influence, allies or territory and still hold the rank of one of the four strongest pirates in the world, is pretty scary.
It’s very unlikely that Shanks has any desire to become Pirate King, because as a former member of the Roger Pirates, he should have the clear advantage when it comes to finding Raftel and knowing the entity of the ‘One Piece’.
One possible endgame goal for Shanks might be that he is ‘guarding’ Raftel and the ‘One Piece’ until a suitable successor of Roger comes into play.
It is possible that Shanks is blocking anyone from nearing Raftel, and he might even be guarding the ‘lost’ Road Poneglyph. If this is his endgame goal, it would explain why he isn’t actively pursuing anything except for having a good time, while still making sure that he and his crew are strong enough to compete with any other pirate crew in the world.