Occasionally I get the “Bluetooth Not Available” message on my MacBook Pro, and it really bugs me. I’ve had it happen 5 times in the last year, and I always have to go back to Google to search for how to fix it. And the fixes I find never seem to work. Then I remember what it was that usually works for me. Here it is:
Unplug your Thunderbolt display cable(s).
Then shut down and restart. Boom!