Authenticator app download

Apple has a built-in authenticator in Passwords.

Go to Settings → Passwords, sign in with TouchID or Passcode.

Find the Account/Website with associated username and code where you would like to add Two-Factor Authentication. Tap in and select Set Up Verification Code... Now you can choose to write the code, or scan the QR code you see when you set up Two-Factor Authentication on a web page.

When the code is scanned, Two-Factor Authentication is set up and saved in Password.

You can find more information here:

How to find saved passwords and passkeys on your iPhone - Apple Support

What are you ranting about?

There is no "Apple Authenticator app".

You can download the Microsoft Authenticator, Google Authenticator, or any number of other 3rd party authenticator apps. Apple doesn't make one.