Custom menu items

You need to have a custom menu enabled in your themes before you can proceed any further. And need to add our own filter into wp_nav_menu_items hook. An example would look like this:

Example code:

add_filter( 'wp_nav_menu_items', 'your_custom_menu_item', 10, 2 );
function your_custom_menu_item ( $items, $args ) {
    if (is_single() && $args->theme_location == 'primary') {
        $items .= '<li>Show whatever</li>';
    }
    return $items;
}

As you can see, you can use the conditional statements along with the argument theme_location. This allows you to target a specific menu location with any condition you want. If you don’t want the conditional statement, you don’t have to use it. Just add it to a specific menu location or vice versa.