code: public function submitForm(array &$form, FormStateInterface $form_state) {
      $installModules = [];
  
      foreach ($form_state->getValues() as $key => $value) {
  
        if (strpos($key, 'install_modules') !== FALSE && $value) {
          preg_match('/install_modules_(?P<name>\w+)/', $key, $values);
          $installModules[] = $values['name'];
        }
      }
  
      $buildInfo = $form_state->getBuildInfo();
  
      $install_state = $buildInfo['args'];
  
      $install_state[0]['thunder_additional_modules'] = $installModules;
      $install_state[0]['form_state_values'] = $form_state->getValues();
  
      $buildInfo['args'] = $install_state;
  
      $form_state->setBuildInfo($buildInfo);
  
    }
docs: {@inheritdoc}