The ANT+ dongle is a suggestion, not a requirement.
For what it’s worth, I’ve been using a Macbook and Bluetooth w/Zwift for a few months now w/out issues.
- Have you tried using the Tacx app on your phone to connect via Bluetooth to your trainer and verify the trainer is working as expected?
- Have you verified that the Bluetooth on your Mac is working fine w/other Bluetooth devices? If so, then it’s probably not your Mac.
- Have you made sure to disconnect or even shutdown Bluetooth on your phone when trying to connect your Mac?
- Have you verified the Flux has the latest firmware?
- Perhaps try Zwift on your phone via Bluetooth to see if that works? If it does, then your trainer probably isn’t the problem.
- Have you opened a support ticket as suggested?
If it worked great for a year, what changed? Did it break after a specific update? You say this is a known problem, care to share the details of said known problem.