You can also sign up for a google account using a non-gmail email address without creating a new gmail address, providing the domain owner hasn't created a workspace account with that domain in the past.

This can be done with an account that you once had control over but don't anymore, like if you leave an employer.

You can't send mail from it, but many apps will take having a google account with a given email is proof of ownership, or an @example.com email address is proof that you are an employee of Example Inc. when they are a customer of the app and have a tenant set up.

You can have a Google ID on any e-mail address, even without workspace. e.g. You don't need gmail to use YouTube.