There are post quantum KEMs though that authenticate with a classical mechanism, which limits quantum attacks to interactive from the previous total breakage of recorded ciphertext exchanges (e.g. Wireshark capture at a router encountered in both directions of the traffic flow).
Google's post-quantum TLS experiments that were done in public via Android Chrome are such; basically you just do normal TLS handshake but stack the key derivation from the traditional DH-type perfect-forward-secrecy exchange with a post-quantum-perfect-forward-secrecy exchange that you all seal under the same handshake authentication, and where you make sure to only use post quantum symmetric primitives to fuse the traditional session key material with the PQ session key material such that you don't rely on either one's resistance to keep your secrets secret.
Sorry I don't have a link quite on hand right now.
Are there? I’ve advocated for such constructions in the past, but I’ve never seen an actual proposal. Do you have a link?