Add a menu item to admin dashboard which isn’t a link? [duplicate]

You may want to look at adding admin style and then targeting the menu:

function admin_style() {
  wp_enqueue_style('admin-styles', get_template_directory_uri().'/admin.css');
}
add_action('admin_enqueue_scripts', 'admin_style');

This is just an example:

#menu-comments:before {
   border-top: 1px solid red;
   content: "";
   display: block;
   margin-top: 10px;
   margin-bottom: 10px;
   width: 100%;
}

This adds a red divider above the “comments” menu, but adjust this to your own requirements.