I am aware others have asked a similar question, but the solution to disable sign-up in the database settings is not helpful.
Since it is not possible to let the user accept Terms & Conditions (TOS) on the Universal Login, it is a requirement to have two different flows:
A) a registration page on which the users MUST accept the TOS before signing up; in this case, the “Sign up” option must be shown on the Universal Login.
B) a login page for users who have already signed up (and accepted the TOS). The Universal Login must NOT show the “Sign up” link because otherwise, new users can use this login to sign up without accepting a TOS.
Though I assume this is not a unique case, I do not know any option to configure the Universal Login to hide the “Sign up”.