You can make a link as a menu item.

In the settings for the link you then set specify an URL.

You can hide the pop-up menu for the level so it is just a "normal" link.

Example:

Here https://pindown.eu/ you can choose the "Help" in the hamburger.

The help is not a page in the project. It is a level that has a link to a sub-project.

Is it something like this you mean?

See this...

1)

2)

Dear John S.

Dear Giuseppe Guida

Thank you for your kind help. 

Did it successfully. 

Regards

Mandar