The article's technique relies on the Domain Registrar providing email forwarding. But I would recommend not using Google Domains. If and when Google's AI bans your gmail account, you lose access to the DNS configurations of your custom domain. And it will be impossible to move the domain to another Registrar because Google Domains will require you to verify ownership with your gmail account, which it has terminated. You can try to do this with a 3rd party domain registrar. Just make sure that your domain's admin account is NOT gmail.

Also, the article assumes that email forwarding is all that you want from a custom domain. Legacy GSuite users may be using other Google features and products, such as Calendar, Contacts, Groups, etc.