Adding custom links, including external to WordPress main menu

Hi

With Drupal CMS one can easily add menu items, like external links, etc, including those that are NOT resulting from Drupal created content as long as one has the URL.

I thought it should be as simple with WP, but simply do not see how I can add this to a WP main menu.
I see on /wp-admin/nav-menus.php the possibility to create new menus but no menu items except if one is just adding one of those shown on the left of the page.

I have seen some few plugins that seem to offer this, but none offered the simple solution I need.

I might have overseen something, so I would appreciate some help.

I urgently need to add some registration page created by some plugin but whose particular page for some reason is not noticed by WP, but I have the url “/directory/add” & I would also probably want to add some external links.

Is there really no solution that needs hard-coding this & that might be overwritten when updating?

Thank you in advance.