How to pass a parameter into a form upon creating?
Just add it to your form's buildForm method signature:

public function buildForm(array $form, FormStateInterface $form_state, $arg = NULL) {
  // Use $arg
}


Then literally pass it to the form builder's getForm method:

$data['form'] = \Drupal::formBuilder()-&gt;getForm('\Drupal\palom_services\Form\ServicesForm', $service_type);