自从evasmat_posted_on() 是主题中的函数，无需使用get_post_meta 获取日期。您可以直接调用该函数，以便：

function evasmat_posts_shortcode(){
    $q = new WP_Query(
        array( \'orderby\' => \'date\', \'posts_per_page\' => \'4\')
    );

    $list = \'<div class="cards">\';

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

        $list .= \'<div class="card">\' .  get_the_post_thumbnail() . \'<h2 class="entry-title-index"><a href="\'.get_permalink().\'">\'.get_the_title() .\'</a></h2>\'  .\'<div class="entry-meta">\' . evasmat_posted_on() .\'</div></div>\';


    endwhile;

    wp_reset_query();

    return $list . \'</div>\';

}

add_shortcode(\'recent-posts\', \'evasmat_posts_shortcode\');