I chose to exclude a dashboard page from the nav in the dashboard but the page was still displayed in the navigation.
I had added a page as belonging to a package:

$sp = SinglePage::add({parentpath}/{pagepath}, $pkg);

under an existing page belonging to the package.

and chose to exclude it from nav:

$sp->setAttribute('exclude_nav', true);

During the package installation.

I checked the page properties on the full sitemap, but the page was still displayed in the navigation at the top of the screen under the parent page at:

/dashboard/{package}/{parentpage}