category link to page

Sorry? You want to do what exactly?

sorry for my english.

this is my website

https://www.opslagunit.nu

there is a link called “Beschikbaar” i want to link this button to this page

https://opslagunit.nu/?page_id=13

and not to a category as it is linked now

Does you theme support custom menus?

yes

So why not create a custom menu. and use the Custom Url option for this menu item?

I have done that but when I visit the website I can’t find the link or the title and it is not a roll over ether

That menu on your site is not a WordPress custom menu. Have you actually added the new custom menu to a location in your theme?