Most message encryption schemes don't use this alone. This is a Key Encapsulation Method (KEM) and it's designed as a way to exchange key information between tw

Most message encryption schemes don't use this alone. This is a Key Encapsulation Method (KEM) and it's designed as a way to exchange key information between two parties, much like Ephemeral Diffie Hellman (EDH) with Ed25519. However many are using Kyber _with_ Ed25519 as a hybrid system. The keying material generates using both schemes are fed into a Key Derivation Function (KDF) to generate a shared symmetric key and then uses AES-GCM or ChaCha20Poly1305 to encrypt any subsequent messages. The reason why we want Kyber is that it's supposed to be post-quantum secure. Ed25519 does not have evidence that it is post-quantum secure, so using a hybrid system does at least guarantee that your scheme is post-quantum ready. The reason you don't immediately switch to Kyber is in case of dodgy initial Kyber implementations, or unknown protocol issues we have not yet discovered.