Get Checkbox Value From Another Form

Create a config file inside your_module/config/install/.

Inside SettingsForm.php write,

$form['#tree'] = TRUE;
$form['clients_enabled'] = array(
  '#title' => t('Enable PixelPin OpenID Connect'),
  '#type' => 'checkboxes',
  '#options' => array('pixelpin' => $this->t('Enable')), 
  '#default_value' => $clients_enabled,
);

public function submitForm(array &$form, FormStateInterface $form_state) {
  $config = $this->config('pixelpin_openid_connect.settings');
  $config->set('clients_enabled_key', $form_state->getValue('clients_enabled'))->save();

}

Inside LoginForm.php, get it :

public function buildForm(array $form, FormStateInterface $form_state) {
$definitions = $this->pluginManager->getDefinitions();
foreach ($definitions as $client_id => $client) {
  foreach ($this->pluginManager->getDefinitions() as $client_name => $client_plugin) {
$is_enabled = isset($this->config('pixelpin_openid_connect.settings')
      ->get('clients_enabled')) ? $this->config('pixelpin_openid_connect.settings')
      ->get('clients_enabled') : false;
    if ($is_enabled) {             
      $url = Drupal::service('path.current')->getPath();

      $find = 'login';

      $pos = strpos($url, $find);

      if ($pos === false){
            $value = 'Register Using @client_title';
        } else {
            $value = 'Log in with @client_title';
        } 

      $element = 'clients_enabled[' . $client_plugin['id'] . ']';
      $form['pixelpin_openid_connect_client_' . $client_id . '_login'] = array(
        '#type' => 'submit',
        '#value' => t($value, array(
          '@client_title' => $client['label'],
        )),
        'visible' => array(
          ':input[name="' . $element . '"]' => array('checked' => TRUE),
        ),
        '#name' => $client_id,
        '#prefix' => '<div>',
        '#suffix' => '</div>',
      );
    }
  }
}
return $form;
}