Yes, it's hashing. But they care, because you can verify if the hash is valid with check-hash. So to precise my question: How can I hash a string in CFML with the blake2b algorythm?

Have you tried looking at https://www.blake2.net? I see two Java libraries listed which is probably your best route.

Yes, I think so, too. Just wanted to be sure not missing a hidden CF feature.