jschauma, Apple goes post-quantum crypto for iMessage, using their new "PQ3" protocol (ML-KEM / Kyber + ECDH for key exchange with periodic (PQC) rekeying:
https://security.apple.com/blog/imessage-pq3/
They also had outside experts do analyses of their new protocol:
https://security.apple.com/assets/files/Security_analysis_of_the_iMessage_PQ3_protocol_Stebila.pdf
https://security.apple.com/assets/files/A_Formal_Analysis_of_the_iMessage_PQ3_Messaging_Protocol_Basin_et_al.pdf