How to get a field third party settings for every content entity forms
Implement hook_field_widget_form_alter() to alter form elements of any content entity form.

For example how to add a validate callback when you have third party settings stored in the field configuration:

/**
 * Implements hook_field_widget_form_alter().
 */
function mymodule_field_widget_form_alter(&amp;$element, FormStateInterface $form_state, $context) {
  $field_definition = $context['items']-&gt;getFieldDefinition();
  if ($field_definition instanceof \Drupal\field\FieldConfigInterface) {
    $mymodule_settings = $field_definition-&gt;getThirdPartySettings('mymodule');
    if (!empty($mymodule_settings)) {
      $element['#mymodule_settings'] = $mymodule_settings;
      $element['#element_validate'][] = 'mymodule_element_validate';
    }
  }

}