WordPress - Add Latest Posts (By Category) To Specific Dropdown Menu Item

wp_add_latest_posts_to_menu_dropdown_v1.php

<?php

function add_latest_post_to_menu_dropdown($items, $menu) {
    if( !is_admin() ) {
        if ($menu->slug == 'the-menu-slug') {
            $post_args = [
                'post_type' => 'post',
                'post_status' => 'publish',
                'numberposts' => 6,
                'category' => 580
            ];

            $order = end($items)->menu_order + 1;
            foreach($items as $i){
                $classes = [];
                foreach($i->classes as $class)
                    $classes[] = $class;
                if ( in_array('show-recents', $classes)) {
                    $recent_posts = wp_get_recent_posts($post_args);
                    $reversed_result = array_reverse($recent_posts);
                    foreach ($reversed_result as $post) {
                        array_unshift($items, _custom_nav_menu_item($post["post_title"], get_permalink($post['ID']), $order, $i->ID));
                        $order++;
                    }
                }
            }

        }
    }
    return $items;
}
add_filter('wp_get_nav_menu_items', 'add_latest_post_to_menu_dropdown', 10, 2);

function _custom_nav_menu_item( $title, $url, $order, $parent = 0 ){
    if($parent == 0 ) $parent = 0;
    $item = new stdClass();
    $item->ID = 1000000 + $order + $parent;
    $item->db_id = $item->ID;
    $item->title = $title;
    $item->url = $url;
    $item->menu_order = $order;
    $item->menu_item_parent = $parent;
    $item->type = '';
    $item->object = '';
    $item->object_id = '';
    $item->classes = array();
    $item->target = '';
    $item->attr_title = '';
    $item->description = '';
    $item->xfn = '';
    $item->status = '';
    return $item;
}