Field formatter with twig editor in settings form

Question

I've created Drupal 9 module with custom field formatter for many field types (string, entity_reference, image etc). I'm trying to implement twig editor in the formatter to control output. I need to have working {{ field_date_range }} {{ field_date_range.end_value }}.

I tried to use $result = $field->view() in viewElements() for field, but when I add any custom variable to field before view it calls error (Element end_value isn't render array). Also, when I did wrap of custom variable to #markup it still visible when I haven't used it in twig.

The question is: Is it possible to implement? If it is, How?

To have better understanding what I'm talking about, I pinned screenshot.

Code:

class CustomTwigFormatter extends FormatterBase {
  public static function defaultSettings() {
    return [
        'custom_markup' => '',
      ] + parent::defaultSettings();
  }
  
  public function settingsForm(array $form, FormStateInterface $form_state) {
    $form = parent::settingsForm($form, $form_state);
    $form['custom_markup'] = [
      '#type' => 'textarea',
      '#title' => $this->t('HTML code'),
      '#description' => $this->t('Twig and HTML tags allowed, e.g: @data', ['@data' => '<div>{{ field_name }}</div>']),
      '#default_value' => $this->getSetting('custom_markup'),
    ];
    return $form;
  }
  
  public function viewElements(FieldItemListInterface $items, $langcode) {
    $elements = [];
    $field_groups = [];
    foreach ($items as $item) {
      $field_groups[$item->getFieldDefinition()->getName()][] = $item->view();
    }
    foreach ($field_groups as $field => $value) {
      $elements[] = [
        '#type' => 'inline_template',
        '#template' => $this->getSetting('custom_markup'),
        '#context' => [
          $field => $value,
        ],
      ];
    }
    return $elements;
  }
}