WordPress nav Walker - Bootstrap 5.2.3 - submenu not opening

Question

I'm trying to integrate WordPress Nav Walker with a two level dropdown, so:

URL
  -URL2
   --URL2
    --URL23

I am using this code:

wp_nav_menu(array(
            'theme_location' => 'main-menu',
            'container' => false,
            'menu_class' => '',
            'fallback_cb' => '__return_false',
            'items_wrap' => '<ul id="%1$s" class="navbar-nav me-auto mb-2 mb-md-0 %2$s">%3$s</ul>',
            'depth' => 0,
            'walker' => new bootstrap_5_wp_nav_menu_walker()
        ));

And this for the nav-walker:

class bootstrap_5_wp_nav_menu_walker extends Walker_Nav_menu
{
  private $current_item;
  private $dropdown_menu_alignment_values = [
    'dropdown-menu-start',
    'dropdown-menu-end',
    'dropdown-menu-sm-start',
    'dropdown-menu-sm-end',
    'dropdown-menu-md-start',
    'dropdown-menu-md-end',
    'dropdown-menu-lg-start',
    'dropdown-menu-lg-end',
    'dropdown-menu-xl-start',
    'dropdown-menu-xl-end',
    'dropdown-menu-xxl-start',
    'dropdown-menu-xxl-end'
  ];

  function start_lvl(&$output, $depth = 0, $args = null)
  {
    $dropdown_menu_class[] = '';
    foreach($this->current_item->classes as $class) {
      if(in_array($class, $this->dropdown_menu_alignment_values)) {
        $dropdown_menu_class[] = $class;
      }
    }
    $indent = str_repeat("\t", $depth);
    $submenu = ($depth > 0) ? ' sub-menu' : '';
    $output .= "\n$indent<ul class=\"dropdown-menu$submenu " . esc_attr(implode(" ",$dropdown_menu_class)) . " depth_$depth\">\n";
  }

  function start_el(&$output, $item, $depth = 0, $args = null, $id = 0)
  {
    $this->current_item = $item;

    $indent = ($depth) ? str_repeat("\t", $depth) : '';

    $li_attributes = '';
    $class_names = $value = '';

    $classes = empty($item->classes) ? array() : (array) $item->classes;

    $classes[] = ($args->walker->has_children) ? 'dropdown' : '';
    $classes[] = 'nav-item';
    $classes[] = 'nav-item-' . $item->ID;
    if ($depth && $args->walker->has_children) {
      $classes[] = 'dropdown-menu dropdown-menu-end';
    }

    $class_names =  join(' ', apply_filters('nav_menu_css_class', array_filter($classes), $item, $args));
    $class_names = ' class="' . esc_attr($class_names) . '"';

    $id = apply_filters('nav_menu_item_id', 'menu-item-' . $item->ID, $item, $args);
    $id = strlen($id) ? ' id="' . esc_attr($id) . '"' : '';

    $output .= $indent . '<li ' . $id . $value . $class_names . $li_attributes . '>';

    $attributes = !empty($item->attr_title) ? ' title="' . esc_attr($item->attr_title) . '"' : '';
    $attributes .= !empty($item->target) ? ' target="' . esc_attr($item->target) . '"' : '';
    $attributes .= !empty($item->xfn) ? ' rel="' . esc_attr($item->xfn) . '"' : '';
    $attributes .= !empty($item->url) ? ' href="' . esc_attr($item->url) . '"' : '';

    $active_class = ($item->current || $item->current_item_ancestor || in_array("current_page_parent", $item->classes, true) || in_array("current-post-ancestor", $item->classes, true)) ? 'active' : '';
    $nav_link_class = ( $depth > 0 ) ? 'dropdown-item ' : 'nav-link ';
    $attributes .= ( $args->walker->has_children ) ? ' class="'. $nav_link_class . $active_class . ' dropdown-toggle" data-bs-toggle="dropdown" aria-haspopup="true" aria-expanded="false"' : ' class="'. $nav_link_class . $active_class . '"';

    $item_output = $args->before;
    $item_output .= '<a' . $attributes . '>';
    $item_output .= $args->link_before . apply_filters('the_title', $item->title, $item->ID) . $args->link_after;
    $item_output .= '</a>';
    $item_output .= $args->after;

    $output .= apply_filters('walker_nav_menu_start_el', $item_output, $item, $depth, $args);
  }
}
// register a new menu
register_nav_menu('main-menu', 'Main menu');

Now I can get the menu to show up. On mobile even to open up. However, I can't get any of the sublevel menu items to show.

My problem is I don't know what to look for. Can't exactly figure out if it is related to css, the walker, or bootstrap in general.

For my menu items with sub-menu, I can see that the aria-dropdown is visible. If I click on them and inspect, I see the following three parameters flashing, like their classes should update, but they don't change:

"nav-link dropdown-toggle" aria-expanded="false"

and the ul under it containing the sub menu also flashes:

"dropdown-menu depth_0"

So nothing changes and I don't receive any errors. Any suggestions are appreciated.

Answer 1

Managed to fix. Bootstrap.js was loaded in footer, causing an issue in the layout. Also, bs nav walker does no work with multilevel nesting. (I had to remove nested items from 2nd level, and the menu started working)