Output HTML after WordPress menu items

functions.php

<?php


//Use nav_menu_item_args hook to add extra HTML to a specific menu item. It will appear inside the <li>
//See $item and $args for other things you can inspect and modify

function mytheme_nav_menu_item_args($args,$item,$depth){

    //print_r($item);
    //print_r($args)
    
    $args->after = '';
    if($item->url == '#custom'){ //only output our HTML when we find a specific link

        $html = '<p>Custom html</p>';        
        $args->after = $html;

    }
    return $args;
}
add_filter('nav_menu_item_args','mytheme_nav_menu_item_args',10,3);

?>