我通过在所有项目中自动添加标记“light”来解决了我的问题。然后用如下方式查询所有带有轻标记的帖子和项目：

按分类标记“light”查询帖子：

$args = array(
   \'post_type\'      => array( \'projects\' , \'post\' ),
   \'tax_query\'      => array(
   \'relation\'       => \'OR\',
        array(
          \'taxonomy\'    => \'post_tag\',
          \'field\'       => \'name\',
          \'terms\'       => \'light\'
        )
     ),
    \'post_status\'   => \'publish\'
);

query_posts( $args );

add_action(\'publish_projects\', \'projects_post_type_tagging\', 10, 2);

function projects_post_type_tagging($post_id, $post){
    wp_set_post_terms( $post_id, \'light\', \'post_tag\', true );
}

您可以在中使用WP\\u查询参数ther tag\\uu来显示与该标记关联的帖子。您可以在此处阅读：https://codex.wordpress.org/Class_Reference/WP_Query#Tag_Parameters

您是否为项目和帖子注册过自定义分类法？这种分类法的鼻涕虫是什么？

$args = array(
             \'post_type\' => array(\'post_type_1\', \'post_type_2\'), 
             \'posts_per_page\' => -1,
             \'post_status\' => \'publish\',
             \'taxonomy-slug\' => \'category-slug\'
);
$query = new WP_Query($args);