As there don't seem to be any PQC alternatives for Diffie-Hellman (DH / ECDH), DH must have been replaced by key encapsulation using an ephemeral key pair. However, since TLS 1.3 always performs ephmemeral key agreement during the handshake I think that it is not possible to directly replace DHE / ECDHE with key encapsulation.
Which changes have been made in the protocol for adjusting it for Post Quantum Cryptography during the testing phase, e.g. using liboqs? Does this alter the TLS specification significantly?