Event on Entity / Node / User ... delete

For this, You must use hook_entity_delete.

Example :
function mymodule_entity_delete(\Drupal\Core\Entity\EntityInterface $entity) {
  $entity_type = $entity->getEntityTypeId();
  $entity_id = $entity->id();
  if ($entity_type === 'node') {
   $node_type = $entity->getType();
   //............
  }
  else if ($entity_type === 'user') {
   //............
 }
}

You can also use the hook_ENTITY_TYPE_delete