To which types do protocols in Swift belong?

Marker Protocols.

// Example of Marker Protocol
protocol Identifiable {
    // Simply indicates that the type is identifiable, without any requirements for methods or properties.
}

Associated Type Protocols.

protocol Container {
    associatedtype Item
    mutating func append(_ item: Item)
    var count: Int { get }
    subscript(i: Int) -> Item { get }
}

Protocols with requirements for methods and properties.

protocol Resizable {
    func resize(to size: CGSize)
    var currentSize: CGSize { get set }
}

These three types describe the main categories of protocols in Swift by their purpose and functionality.