how to add a non-visible page

Yes it’s possible but you either need to exclude the page via the wp_list_pages or wp_page_menu template tag or create a custom menu that simply omits this page.

I had the exact same question, thanks! Now, with the wp_list_pages or the wp_page_menu, do you simply add that to your style sheet and then modify it? Or what exactly do you do?

It’s a template tag in your theme’s navigation template file(s). You need to examine your theme’s template files and find which of these tags is being used. Then add the appropriate exclude parameter with the correct id for the page you want to exclude.

Thank you!