Hey @manfredicops,
Yes there’s a Current state that you can use to style the navigation items with an underline which will show up if they are on that particular page. If for some reason, you are not able to see the “Current” state for navigation links, you could try out this workaround to see if it solves the issue.
Alternatively, you could target such elements via custom CSS, if you prefer it that way by targeting navigation items with the class .w--current which is the class that gets applied when the navigation item points to the current page. So you can apply the custom CSS by targeting elements with that class and it should solve your use-case. Hope this helps.