我不确定您是否有带有类别的页面，但我可以向您展示一个使用帖子的示例。

按类别从帖子中下拉筛选：

<?php

    $url = get_home_url();
    $category_slug = \'my-new-category\'; //remember to get the slug


    $posts_by_category = new WP_Query([
        \'post_type\' => \'post\',
        \'category_name\' => $category_slug,
        \'nopaging\' => true
    ]);


    if ( $posts_by_category->have_posts() ) :
        $dropdown = \'<select onchange="window.location.href = this.value" name="posts-by-category">\';

        while ( $posts_by_category->have_posts ) : $posts_by_category->the_post();

            $dropdown .= sprintf(\'<option value="%s?p=%s">%s</option>\', $url, get_the_ID(), get_the_title() );

        endwhile;

        $dropdown .= \'</select>\';

    endif; wp_reset_postdata();

    echo $dropdown;

?>