Bluetooth unavailable, SMC reset
After disconnecting my JBL Bluetooth speakers from my 2009 Intel Macbook Pro, running Catalina (patch), my Bluetooth became unavailable: the Bluetooth logo in the menu bar has a dash through it and the Bluetooth icon was missing from Systems prefs.
I did a SMC (System Management Controller) reset, as mentioned in this Bluetooth missing from system preferences? - Apple Community thread.
Shut down your Intel macbook pro, disconnect everything, hold down SHIFT/CONTROL/OPTION and then press the power button. Hold all 4 keys for 5-6 seconds and release.
Bluetooth is back, worked like a charm.
Earlier Mac models