iOS (and MacOS) now use Google’s BoringSSL instead and have for many years
Or comments such as: https://github.com/apple-oss-distributions/Security/blob/rel...
Unsurprisingly, given BoringSSL doesn't have a stable API (yet alone ABI), it isn't exposed as a system library.
If you really are doubting what gets used for TLS, open up Console.app, start streaming, run `nscurl https://example.com/` (or load it in Safari, etc.), and you'll see logging like:
default com.apple.network boringssl 18:11:46.229209-0700 libboringssl.dylib nscurl boringssl_session_apply_protocol_options_for_transport_block_invoke(2360) [C1.1.1.1:2][0x1008cef10] TLS configured [server(0) min_version(0x0303) max_version(0x0304) name(redacted) tickets(false) false_start(false) enforce_ev(false) enforce_ats(false) ats_non_pfs_ciphersuite_allowed(false) cc_mode_enforced(false) ech(false) pqtls(true), pake(false)]
It really is boringssl which is nowadays used for TLS by the Network framework.