Hide items in left nav bar

You could do this via an Admin Theme.

Another way is to totally yoink the page from the menu… for instance I never ever use the links manager… so

// GET RID OF THE LINKS MANAGER I HAVEN"T USED IT IN YEARS
add_action( 'admin_menu', 'voodoo_admin_menu' );

function voodoo_admin_menu() {
	remove_menu_page('link-manager.php');
}

added to functions.php or better yet a functionality plugin totally removes the links page from the menu