Thanks for the information. Unfortunately, I was not able to fully understand this. I got stuck where it says:
However, this is not enough, because the wordpress template tag comments_template() has some check build-in,
to make sure that comments are normally only be displayed either on a single article or page.
Find this in /wp-includes/comment-template.php line 858:
view source print?
1 if ( !(is_single() || is_page() || $withcomments) || empty($post) )
2 return;
The code provides the use of a global variable $withcomments that can be set to boolean true (or 1) to allow the display
of comments.
I did not understand where to find: /wp-includes/comment-template.php line 858.