class MediaLibraryInceptionWidget

class MediaLibraryInceptionWidget extends MediaLibraryWidget {
  
  /**
   * {@inheritdoc}
   */
  public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
    if (empty($element['#element_validate'])) {
      $element['#element_validate'] = [];
    }
    $element['#element_validate'][] = [
      $this,
      'elementValidate',
    ];
    return parent::formElement($items, $delta, $element, $form, $form_state);
  }
  
  /**
   * {@inheritdoc}
   */
  public function elementValidate($element, FormStateInterface $form_state, $form) {
    $field_name = $element['#field_name'];
    $entity = $form_state->getFormObject()
      ->getEntity();
    $input = $form_state->getUserInput();
    if (!empty($input['_triggering_element_name']) && str_contains($input['_triggering_element_name'], 'media-library-update')) {
      // This will validate a required field before an upload is completed.
      $display = EntityFormDisplay::collectRenderDisplay($entity, 'edit');
      $display->extractFormValues($entity, $form, $form_state);
      $display->validateFormValues($entity, $form, $form_state);
    }
    $form_value = $form_state->getValue($field_name);
    if (!empty($form_value['media_library_selection'])) {
      $entity->set($field_name, $form_value['media_library_selection']);
    }
  }

}