entity_delete_protect.module

<?php

use Drupal\user\Entity\User;
use Drupal\Core\Entity\EntityInterface;
use Drupal\Core\Session\AccountInterface;

/**
 * Implements hook_entity_access().
 */
function entity_delete_protect_entity_access(EntityInterface $entity, $operation, AccountInterface $account) {
  if ($operation === 'delete' && $entity->access('view', User::getAnonymousUser()) {
    return AccessResult::forbidden();
  }
  else {
    return AccessResult::neutral();
  }
}

/**
 * Implements hook_entity_predelete().
 */
function entity_delete_protect_entity_predelete(EntityInterface $entity) {
  if ($entity->access('view', User::getAnonymousUser()) {
    throw new \RuntimeException("Unable to delete entity because it is visible to anonymous users.")
  }
}