How do I flag emails with different colored flags on iPhone?

Sign in with Apple uses an existing Apple ID to quickly and securely sign in to websites, apps, and services. To access an account using Sign in with Apple, just tap the button and confirm your identity with Face ID or Touch ID.
Sign in with Apple can be used anywhere you can access an account, app, or service. This means Sign in with Apple works on web browsers, Android and Windows apps, and all Apple devices.
Sign in with Apple can be used anywhere, as long as the app or website offers Sign in with Apple as a sign in method.
Sign in with Apple automatically requires two-factor authentication (2FA) to protect your Apple ID. This means every account or app logged into using Sign in with Apple is also protected by 2FA.
Sign in with Apple can be used to sign up for a service, app, or website. When creating a new account, Sign in with Apple offers the option to share or hide your real email address.
During the sign up process, tap the radio button next to Hide My Email. Apple will create a new email address for the account, which automatically forwards messages to your real email address.