[Update] 找到的解决方案：

我在找\'items_wrap\' => \'<ul id="%1$s" class="%2$s" role="menu" >%3$s</ul>\'

    <?php
        wp_nav_menu( array(
            \'menu\'              => \'menu\',
            \'theme_location\'    => \'menu\',
            \'items_wrap\' => \'<ul id="%1$s" class="%2$s" role="menu" >%3$s</ul>\',
            \'depth\'             => 0,
            \'container\'         => \'\',
            \'menu_class\'        => \'dropdown-menu\',
            \'fallback_cb\'       => \'wp_bootstrap_navwalker::fallback\',
            \'walker\'            => new wp_bootstrap_navwalker())
        );
    ?>