Correct way to retrieve comment attributes for desired results

First off, the get_comment_date( 'd\/m\/Y' ) resulted in a PHP notice in my case, so I changed that to get_comment_date( 'd\/m\/Y', $comment ) (i.e. I pass the $comment object to the function).

Now the issue with your code is that the $result should have a review item with the value being an array of reviews (review objects):

$result = [
  "@context" => "https://schema.org/",
  "@type" => "Organization",
  "name" => (get_the_title()),
  "image" => (get_the_post_thumbnail_url(get_the_ID(), 'full')),
  "aggregateRating" => [
    ...
  ],
  'review' => $comlistall, // here, a "review" item must exists
/* Or something like so:
  'review' => array(
    array( "@type" => "Review", "headline" => ..., "reviewbody" => ..., ... ),
    array( "@type" => "Review", "headline" => ..., "reviewbody" => ..., ... ),
    ...
  ),
*/
];

Secondly, your $comlistall should produce an array which when it’s represented in JSON format, looks like the first one here (see the “Changed Text”).

So to fix the issue:

1. As I mentioned above, in the $result, use 'review' => $comlistall.

2. Change this:

   $c = [ "review" => [
     "@type" => "Review",
     "headline" => (get_comment_meta($comment->comment_ID, WP_REVIEW_COMMENT_TITLE_METAKEY, true)),
     "reviewbody" => ($comment->comment_content),
     ...
   ] ];
   $comlistall[] = $c;
   

   to this (but you may assign the review data/object to the variable $c):

   $comlistall[] = [
     "@type" => "Review",
     "headline" => (get_comment_meta($comment->comment_ID, WP_REVIEW_COMMENT_TITLE_METAKEY, true)),
     "reviewbody" => ($comment->comment_content),
     ...
   ];