What's the issue? Everything in TLS, including versions 1.2 and 1.3 is sent using data records with a limit in size. That limit was established long ago, but PQC algorithms may have larger public key sizes and cyphertexts. So, a modification to TLS1.3 might be needed to allow for larger data records.
The discussion section of the "Hybrid key exchange in TLS 1.3" draft RFC (https://lnkd.in/da5vbMac, draft-ietf-tls-hybrid-design-09) by Douglas Stebila, Scott Fluhrer and Shay Gueron explains that, although some post-quantum KEMs have larger public keys and/or ciphertexts (Classic McEliece's smallest parameter set has public key size 261,120 bytes), all defined parameter sets for Kyber have public keys and ciphertexts that fall within the TLS constraints (2^16-1 bytes).