Programmatically create a comment form for a node
FormBuilder::getForm() doesn't accept just an argument; after the first, the other arguments are:


  Any additional arguments are passed on to the functions called by \Drupal::formBuilder()->getForm(), including the unique form constructor function. For example, the node_edit form requires that a node object is passed in here when it is called. These are available to implementations of hook_form_alter() and hook_form_FORM_ID_alter() as the array $form_state->getBuildInfo()['args'].


So, \Drupal::formBuilder()-&gt;getForm('Drupal\comment\CommentForm', $node); would be perfectly fine. It's up to the form builder, using those arguments.