I'm working on Apple Sign In in Simulator iOS 13.4.1 and XCode Version 11.4.1.
I used to get privaterelay.appleid.com when Hide Email before but after changing my Laptop and try to test Apple Sign In in Simulator again, I got nil result. For other email when I didn't activate Hide Email it's still working and not give me any nil result.
Here my code:
// Create class for object first
class AppleUser{
    var id: String?
    var firstName: String?
    var lastName: String?
    var email: String?
    @available(iOS 13.0, *)
    init(credentials: ASAuthorizationAppleIDCredential) {
        id = credentials.user
        firstName = credentials.fullName?.givenName ?? ""
        lastName = credentials.fullName?.familyName ?? ""
        email = credentials.email ?? ""
    }
}
extension AppleUser: CustomDebugStringConvertible{
    var debugDescription: String{
        return """
        ID: \(id ?? "")
        First Name: \(firstName ?? "")
        Last Name: \(lastName ?? "")
        Email: \(email ?? "")
        """
    }
}
    // on ViewController
    @objc
    func didTapAppleButton(){
        if #available(iOS 13.0, *) {
            let provider = ASAuthorizationAppleIDProvider()
            let request = provider.createRequest()
            request.requestedScopes = [.fullName, .email]
            let controller = ASAuthorizationController(authorizationRequests: [request])
            controller.delegate = self
            controller.presentationContextProvider = self
            controller.performRequests()
        } else {
            // failed
        }
    }
extension ViewController: ASAuthorizationControllerDelegate, ASAuthorizationControllerPresentationContextProviding{
    @available(iOS 13.0, *)
    func presentationAnchor(for controller: ASAuthorizationController) -> ASPresentationAnchor {
        return view.window!
    }
    func authorizationController(controller: ASAuthorizationController, didCompleteWithAuthorization authorization: ASAuthorization) {
        switch authorization.credential {
        case let credentials as ASAuthorizationAppleIDCredential:
            let user = AppleUser(credentials: credentials)
            print(user)
            /*
            Print result when Hide Email
            ID: 123215213243.e12324213.12314213 <some random Int>
            First Name: My First Name
            Last Name: My Last Name
            Email: <nil>
            Print result when normal Email used
            ID: 123215213243.e12324213.12314213 <some random Int>
            First Name: My First Name
            Last Name: My Last Name
            Email: my_email@icloud.com
            */
        default:
            // failed
        }
    }
}