How can I load entity form for comment?
it also needs the field name I think, check CommentDefaultFormatter::viewElements

https://api.drupal.org/api/drupal/core%21modules%21comment%21src%21Plugin%21Field%21FieldFormatter%21CommentDefaultFormatter.php/class/CommentDefaultFormatter/8

It uses a lazy builder so it can be built after render caching 

$output['comment_form'] = [ '#lazy_builder' => ['comment.lazy_builders:renderForm', [ $entity->getEntityTypeId(), $entity->id(), $field_name, $this->getFieldSetting('comment_type'), ]], '#create_placeholder' => TRUE, ];