Make it compatible with Webform v6

https://www.drupal.org/project/webform_encrypt/issues/3142997 📌 Webform Encrypt D9 readiness Fixed
This patch fixes the issue.

But when saving the form I still having another new fatal error.

Thanks for testing @paul_leclerc
Can you tell me what's the error. May be I can look into it.

The new error append when sending the webform.

Drupal\Core\Entity\EntityStorageException: in Drupal\Core\Entity\Sql\SqlContentEntityStorage->save() (line 815 of core/lib/Drupal/Core/Entity/Sql/SqlContentEntityStorage.php).
Drupal\encrypt\EncryptService->encrypt() (Line: 122)
Drupal\webform_encrypt\WebformEncryptSubmissionStorage->encrypt() (Line: 74)

I could trace the error until Key.php > loadFromAsciiSafeString > return new Key($key_bytes); (l51)

Interesting, this patch works fine for me. Are you using the patch uploaded here https://www.drupal.org/project/webform_encrypt/issues/3142997 📌 Webform Encrypt D9 readiness Fixed on the other issues?