Correct answer! Preferences is now called Settings. It has no indication for Bluetooth Output at first, but the term System is the item to select to create the BlueTooth connection. The BlueTooth Device's name will appear in the audio output options with this path:
At the menu bar: GarageBand > Settings > Midi/Audio > Output Device: Output > System Setting > make device available for connection > BlueTooth > connect device > audio should begin to output to Bluetooth device > device name appears under System Setting Output choices.
My GB project sounds much better than what the little internal speakers can output and better than my headphones can output, once it is output by hi fi speakers.
Thank you.