menu_position is not used when you set show_in_menu to a submenu.
to put your menu in last position there is 2 solutions.
The first is to change the menu construction priority like this :
add_action("admin_menu", function () {
remove_action('admin_menu', '_add_post_type_submenus');
add_action( 'admin_menu', '_add_post_type_submenus', 200);
// 200 to set it after the last element of WooCommerce which as the priority 70
}, 1);
With this, all custom post types are modified. If this is not what you want, the 2nd solution is to set show_in_menu to FALSE and to create the submenu by yourself with https://developer.wordpress.org/reference/functions/add_submenu_page/