EntityDateFormat.php

<?php

namespace Drupal\system\Plugin\migrate\destination;

use Drupal\Core\Datetime\DateFormatInterface;
use Drupal\Core\Entity\EntityInterface;
use Drupal\migrate\Plugin\migrate\destination\EntityConfigBase;

/**
 * @MigrateDestination(
 *   id = "entity:date_format"
 * )
 */
class EntityDateFormat extends EntityConfigBase {
    
    /**
     * {@inheritdoc}
     */
    protected function updateEntityProperty(EntityInterface $entity, array $parents, $value) {
        assert($entity instanceof DateFormatInterface);
        if ($parents[0] == 'pattern') {
            $entity->setPattern($value);
        }
        else {
            parent::updateEntityProperty($entity, $parents, $value);
        }
    }

}