There is a section called Menu Items in the portal where you can add more menus in the portal header.
Custom Menu Item URL Type
It specifies where the URL for a menu item will come from. If you choose the Airtable Field option as the Custom Menu Item URL Type, you will be able to select a field from the user table to use as the source for the URL.
Custom Menu Item Type
Meanwhile, you can select whether to open the link in a new tab or embed it in the portal by setting Custom Menu Item Type for each menu.