code: private function findOrphanedIdentitiesByGroup(array $group)
      {
          $identifiers = array_column($group, 'objectIdentifier');
  
          $allIdentities = $this->identityService->findBy([
              'adapterName' => $group[0]['adapterName'],
              'objectType' => $group[0]['type'],
          ]);
  
          return array_filter($allIdentities, function (Identity $identity) use ($identifiers) {
              return !in_array($identity->getObjectIdentifier(), $identifiers, true);
          });
      }
docs: @param array $group
  
  @return Identity[]