How to display sign up /login at the top right

The URL for the login is always of the form:

https://yoursite.com/path-to-your-wp-installation/wp-login.php

The URL for the sign up is:

https://yoursite.com/path-to-your-wp-installation/wp-login.php?action=register

Just add suitable HTML for those URLs, styled as you’d like them. The HTML will probably have to go in header.php and the CSS in style.css, if your theme uses standard conventions.

You can also use CSS to hide/unhide the html as appropriate depending on whether the user is logged in or not. So logged-in users get a welcome of whatever; and users who are not logged in get the links.

You should, of course, do all this in a child theme.

HTH

PAE