How to add Plugin functionality in WordPress Frontend Menus

At the time of registering taxonomy, make sure you use the show_in_nav_menus parameter and set it true.

For Example:

 $args = array(
        'label'             => __( 'book', 'textdomain' ),
        'public'            => true,
        'rewrite'           => array('slug' => 'book', 'with_front' => true),
        'hierarchical'      => true,
        'show_in_nav_menus' => true,
        'show_ui'           => true,
    );

register_taxonomy( 'book', 'products', $args);