如果有人需要，这是我找到的解决方案。

add_filter('wp_all_import_is_post_to_create', 'create_only_if_unique_custom_field', 10, 3);
function create_only_if_unique_custom_field( $continue_import, $data, $import_id ) { 
    // Only run for import ID 33 and 34
    if ( $import_id == 33 ) {
    
    // Xml file column name
    $value = $data['name'];
        
    // Get wpdb product title
  $posts = get_posts([
    'post_type'  => 'product',
    'title' => $value,  
  ]);
    
    return !$posts;

    } else {
       // Take no action if a different import ID is running.
       return $continue_import;
    }
}