Base on the warning message form auth0 dashboard pages, it mentions
Blockquote
“WebAuthn, Voice message, and Email are not available as authentication factors when using the Classic Universal Login experience and when using a custom Multi-factor Authentication page.”,
email can’t be used as mfa factor when classic universal and custom mfa page are used.
Is there a way to use email as mfa factor and also be able to customize the mfa page?
I’m afraid there isn’t a way to do this currently, it is only supported in the New Universal Login.
However, the New Universal Login does have a lot of customisation options available via it’s API endpoints, you can modify the text and the HTML surrounding the widget too (the latter requires using a custom domain however), please see here for more information: