/**
 * Implements hook_entity_update().
 */
function {{ machine_name }}_entity_update(Drupal\Core\Entity\EntityInterface $entity) {
  // Update the entity's entry in a fictional table of all entities.
  \Drupal::database()->update('example_entity')
    ->fields([
      'updated' => REQUEST_TIME,
    ])
    ->condition('type', $entity->getEntityTypeId())
    ->condition('id', $entity->id())
    ->execute();
}