Drupal 8 - hook update - installEntityType/uninstallEntityType

mymodule.php

<?php

/**
 * Update- Create your_entity_name entity.
 */
function my_module_update_8001() {
  //check if the table exists first.  If not, then create the entity.
  if(!db_table_exists('your_entity_name')) {
    \Drupal::entityTypeManager()->clearCachedDefinitions();
    \Drupal::entityDefinitionUpdateManager()
      ->installEntityType(\Drupal::entityTypeManager()->getDefinition('your_entity_name'));
  }
  else {
    return 'your_entity_name entity already exists';
  }
}

/**
 * Uninstall- Create your_entity_name entity.
 */
function my_module_update_8003() {
  //check if the table exists first.  If not, then create the entity.
  if(db_table_exists('your_entity_name')) {
    \Drupal::entityTypeManager()->clearCachedDefinitions();
    \Drupal::entityDefinitionUpdateManager()
      ->uninstallEntityType(\Drupal::entityTypeManager()->getDefinition('faq_answer_entity'));
  }
  else {
    return 'faq_answer_entity entity do not exist';
  }
}

Since Drupal 8.7.x, drush entup and automatic entity updates have been removed.

2 ways :

• https://www.drupal.org/project/devel_entity_updates
• hook_update