Hello @KCTRUSTED !

If you want to left the Sign up page visible only for the guests then it needs to visit the Studio->Pages->System->Sign up page, Settings->Visibility tab and set the value only as the "Unauthenticated" variant.

In your case, it seems you changed the visibility of the very field in the Studio->Forms->System->Accounts->5 displays->Create account area. You need to reverse all them back.