There is a section called Menu Items in the portal where you can add external links and embeds (e.g. Airtable views) 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.