There is a port of Mbed TLS to Classic MacOS[1] which has TLS 1.2 enabled but per the README.md probably not the right cihper suites (it only has AES-CBC ciphers enabled by default) to connect to servers configured per the widely-used Mozilla "intermediate" recommendations[2] (which require AES-GCM or ChaCha20 ciphers).

[1] https://github.com/bbenchoff/MacSSL [2] https://wiki.mozilla.org/Security/Server_Side_TLS