mDNS broadcast doesn’t work on macOS 27 (Local Network permissions don’t transfer from the launcher to the game app) when using the usual Zwift launcher (Zwift icon), so the JetBlack is not found on the local network, and you cannot connect using Wi-Fi to the trainer.
The workaround for now is to launch the app directly from the Terminal. The app executable is “$HOME/Library/Application Support/Zwift/ZwiftAppSilicon”; make sure you give permissions to access Local Network to Terminal when requested, and you are good to go.
I thought like sharing as it made me waste a few hours until I found the issue.
BTW, this probably happens with Wahoo trainers as well.