Force Drupal to show what timezone a date is being set in 😑

muh_module.php

<?php

/**
 * Implements template_preprocess_fieldset().
 */
function muh_module_preprocess_fieldset(&$variables) {
  // Figure out if this is a "date field" fieldset
  $hasElementValueType = isset($variables['element']) && isset($variables['element']['value']) && isset($variables['element']['value']['#type']);
  if ($hasElementValueType && $variables['element']['value']['#type'] == 'datetime' && isset($variables['element']['value']['#date_timezone'])) {
    // Show what timezone the date field is using as the fieldset description
    $timezone = $variables['element']['value']['#date_timezone'];
    if (!empty($timezone)) {
      $variables['description_display'] = 'after';

      $variables['description']['content'] = new TranslatableMarkup(
        'Date will be set in %timezone timezone',
        array(
          '%timezone' => $timezone
        )
      );
    }
  }
}