How to programmatically render a contact form in a theme in D8
Contact form is an entity, but you can't view it.

What you want instead is an add form of a contact_message with contact_form as bundle.

See ContactController::contactSitePage() (EDIT: API docs) as example:

$message = \Drupal::entityTypeManager()
  -&gt;getStorage('contact_message')
  -&gt;create(array(
    'contact_form' =&gt; $contact_form-&gt;id(),
  ));

// This works in a controller, use \Drupal::service('entity.form_builder') elsewhere.
$form = $this-&gt;entityFormBuilder()-&gt;getForm($message);
$form['#title'] = SafeMarkup::checkPlain($contact_form-&gt;label());


EDIT (thanks @nilsun): Note that entityManager is deprecated in favour of entityTypeManager.