Remove reply link in comments
You could use the hook_comment_links_alter()

use Drupal\comment\CommentInterface;

/**
 * Implements hook_comment_links_alter().
 * 
 * Unsets the "Reply" link of a comment.
 * 
 * @param array &amp;$links
 *   A renderable array representing the comment links.
 * @param \Drupal\comment\CommentInterface $entity
 *   The comment being rendered.
 * @param array &amp;$context
 *   Various aspects of the context in which the comment links are going to be
 *   displayed, with the following keys:
 *   - 'view_mode': the view mode in which the comment is being viewed
 *   - 'langcode': the language in which the comment is being viewed
 *   - 'commented_entity': the entity to which the comment is attached
 */
function mymodule_comment_links_alter(array &amp;$links, CommentInterface $entity, array &amp;$context) {
  // Unset the "Reply" link
  if(isset($links['comment']['#links']['comment-reply'])) {
    unset($links['comment']['#links']['comment-reply']);
  }
}