How to move the comment form to the top?
You can in field--comment.html.twig

{#
/**
 * @file
 * Default theme override for comment fields.
 *
 * Available variables:
 * - attributes: HTML attributes for the containing element.
 * - label_hidden: Whether to show the field label or not.
 * - title_attributes: HTML attributes for the title.
 * - label: The label for the field.
 * - title_prefix: Additional output populated by modules, intended to be
 *   displayed in front of the main title tag that appears in the template.
 * - title_suffix: Additional title output populated by modules, intended to
 *   be displayed after the main title tag that appears in the template.
 * - comments: List of comments rendered through comment.html.twig.
 * - content_attributes: HTML attributes for the form title.
 * - comment_form: The 'Add new comment' form.
 * - comment_display_mode: Is the comments are threaded.
 * - comment_type: The comment type bundle ID for the comment field.
 * - entity_type: The entity type to which the field belongs.
 * - field_name: The name of the field.
 * - field_type: The type of the field.
 * - label_display: The display settings for the label.
 *
 * @see template_preprocess_field()
 * @see comment_preprocess_field()
 */
#}
&lt;section{{ attributes }}&gt;
  {% if comments and not label_hidden %}
    {{ title_prefix }}
    &lt;h2{{ title_attributes }}&gt;{{ label }}&lt;/h2&gt;
    {{ title_suffix }}
  {% endif %}

  {{ comments }}

  {% if comment_form %}
    &lt;h2{{ content_attributes }}&gt;{{ 'Add new comment'|t }}&lt;/h2&gt;
    {{ comment_form }}
  {% endif %}

&lt;/section&gt;


So copy the above code and go to /themes/YOURTHEME/templates folder and create field--comment.html.twig and now paste code.

Now, all you gotta do is just move

 {% if comment_form %}
    &lt;h2{{ content_attributes }}&gt;{{ 'Add new comment'|t }}&lt;/h2&gt;
    {{ comment_form }}
  {% endif %}


and place it above the {{ comments }} line

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