Need help to embed Block-Element via shortcode (NH-site)

Hello,

on this site , I have created a Block-Element as a custom-hook-name "trainer1", display on "Entire Site".

Then I added the following code to the child-themes function.php:

function mb_shortcode1($atts, $content = null) {
      ob_start();
      do_action('trainer1');
      return ob_get_clean();
}
add_shortcode('trainer1_code', 'mb_shortcode1');

Finally, on this page I have added the shortcode [trainer1_code] as the last content block, and expected the Block-Element to be displayed, but it does not work.

Can you please help me troubleshooting this? Just in case I have admin-auto-login credentials in private notes field below.

Thanks in advance and kind regards
Sascha