You would draw all those paths and then use the Live Paint tool to fill in the shapes.
But how do I get it so smooth and symmetrical?
"But how do I get it so smooth and symmetrical?"
You are seeing asymmetries that give the impression of an underlying symmetry, with some symmetrical key parts.
To create something equivalent, you can start out with the (simple) underlying symmetrical artwork, then change and elaborate.
Anything that's truly symmetrical is just one side drawn, then duplicated and reflected. The smoothness is a matter of learning and practicing the Pen tool, along with refinement after the fact.
I would draw the shapes with the pen tool. Then they are using gradient fills to create the depth of the shape.
Tried to buy got real messy 😭
I applied effect > warp > flag twice as once was nto enought
Or you can use puppet warp tool to do the wave distortion.