What kind of implication does `any` have on concrete generic protocol types?

Question

I want to understand the implications of any when using specialized generic protocols in Swift. Here is my code:

protocol ShapeA {
}

protocol ShapeB {
    associatedtype AAA
}

protocol BaseC<T> {
    associatedtype T
}

protocol ShapeC: BaseC<Int> {
}

protocol Maker {
    func makeShapeA() -> ShapeA
    func makeShapeB() -> any ShapeB
    func makeShapeC() -> any ShapeC
}

• Why does makeShapeC requires any before return type? From my perspective ShapeC is a protocol that is fully specified, just like ShapeA. What exactly is the difference?
• Why doesn't makeShapeA require any? It's existential type just according to the descriptions that I find online...
• In case I leave the code as it is: is there an actual performance difference between makeShapeA and makeShapeC as they both return existential types as far as I can tell?