Recently, there are more opportunities to see the "Sign in with Apple" screen in apps that require sign-in. As far as I can read the explanation, it seems that the procedure is speedy and privacy is protected, and it is not necessary to disclose the e-mail address … Why so suddenly increased?
This "Sign in with Apple" is Apple's official user authentication system, supported on iOS 13 and later. Apps compatible with this system can sign in to an app / service or register a new one using Face ID or Touch ID without having to enter an email address (user ID) or password each time.
The Apple ID uses "two-factor authentication" that allows you to log in unless you use your other device in addition to your email address and password to achieve high security. By providing development tools and making this authentication mechanism available to the application, we will try to improve the security of the entire iOS application that requires sign-in.
The reason why the number of compatible apps is increasing rapidly is that the support for "Sign in with Apple" is now mandatory for third-party apps that require sign-in. If you do not support it, distribution in the App Store may not be accepted, so the number of compatible apps is increasing from the latter half of 2019.
The deadline for signing in with Apple was originally set at the end of April 2020, but was extended to the end of June 2020. Due to the spread of the new coronavirus and the impact on the economy, there are some uncertainties about the future, but apps that require sign-in will always be supported. The "Sign in with Apple" screen will be viewed more and more in the future.