Our assembler for macOS is very old and doesn't support newer instructions such as SHA-NI. This means we have to disable such features in GnuTLS and nettle when compiling for that platform.
Fortunately we don't use GnuTLS at all on the client currently, and we only perform a few SHA hashes, so this is currently not a problem in practice. It might be in the future though if we start doing more TLS traffic in the client (e.g. using WebSockets instead of SSH).
Note that even in such a future this might still not be a big issue since ChaCha is currently preferred over AES, and who knows what is popular next.