pancakes07 there's no easy way to do that. Flarum and many extension rely on the email as a unique user identifier.
If you are building an integration, you can generate a fake but unique email for each user, set isEmailConfirmed to true when creating the user via the API and set the mail driver to null to prevent any outbound email from being sent.
You can then hide any reference to email in Flarum UI using custom CSS or an extension (this extension hides the email notification column from the notification grid https://discuss.flarum.org/d/30634-no-email-notifications)
