413 Request Entity Too Large – navmenus.php

I want to create a new page in a wordpress (org) that I can link to, but I do not want that page to automatically become a tab on my menu. How to do?

I have the error
“413 Request Entity Too Large

The requested resource
/sfrua/wp-admin/nav-menus.php
does not allow request data with GET requests, or the amount of data provided in the request exceeds the capacity limit.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.”