1. Setup a backup email for recovery
2. Copy paste and save Backup Codes somewhere remote
3. If you are using an app like "Google Authenticator", they have an easy way to Export the settings on another phone. Do it on your wife's/gf's/family/sibling etc phone and that way you have another backup of 2FA codes.
4. Do not use the "Google Prompt" option because that only works on primary device.
Google didn't invent any of this, it is fully standardized (see RFC6238). There are lots of fully compatible alternatives with better options for security and backup and restore.
Personally, I use FreeOTP+ with a password lock and secret keys backed up off device.
Secondary opinion, why is the Google app lacking? Because they really don't want people to use it. They much prefer you reveal your phone number and use SMS instead. This way they can easily identify you personally.
Remember, everything Google does is subtly designed to help violate your privacy in some way. The quickest way to convince me not to use an app is to put a "Google" label on it.
Sure, companies may do some evil things intentionally, but an app UI sucking is usually the default state of things and not some malice necessarily. In this case, I think part of the neglect of Google Authenticator is them trying for years to pivot to other forms of two-factor authentication that are more phishing-resistant than an OTP (Yubikey-like and smartphone based systems).
Yes, that probably explains why they prefer OTP over SMS --- because it is more secure --- and it totally violates your privacy.
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.