You can set a backup email address for Google accounts if they're using Google email addresses, but you can't do this if they're using non-Google email addresses as the primary address, such as the one in that link.

I'm logged in to such an account right now and there's no way to do this. The account primary email is also set as the recovery email address and there's no way to add another.

It's actually deceptive to the user to even call it a recovery email address in this case, since Google will never offer to alternatively send a verification code there if the 2FA device is unavailable.

I lost access to a Gmail account for which I had the correct password and a recovery email with a different email service. I was still unable to convince the Google machine that the account was mine. My suspicion is that because I'd changed operating systems on my desktop, I appeared to be 'someone else' as far as Gmail was concerned.