Hello @emurphy,
It is not possible to hide the Sign Up button right off the bat when using the New Universal Login. Still, it may be doable and the following Knowledge Solution should make the issue clear for you:
https://community.auth0.com/t/hide-the-sign-up-link-conditionally-when-using-the-new-universal-login/139077
I hope this was helpful and if you have other questions please don’t hesitate to ask.
Thank you,
Tudor