经过几个小时的谷歌搜索，我想出了以下解决方案。也许一次对某人有帮助。

1） 查询帖子使用gutenberg youtube块的位置：

$args = array(
    \'post_type\'         => \'post\',
    \'post_status\'       => \'publish\',
    \'s\'                 => \'core-embed/youtube\',
    \'posts_per_page\'    => 1
);

$query = new WP_Query($args);

$post_id = 117;
$post = get_post($post_id);
$blocks = parse_blocks( $post->post_content );


function findYoutubeBlock(array $blocks) {
    return $blocks[\'blockName\'] == \'core-embed/youtube\';
}


if (has_block(\'core-embed/youtube\', $post_id)) {
    $youtube_block = reset(array_filter($blocks, \'findYoutubeBlock\'));
    $youtube_url =  $youtube_block[\'attrs\'][\'url\'];
}