How to get Mac and Bluetooth in place

Activate the Bluetooth menu by holding down Shift+Alt simultaneously, the command we are interested in appears: Debug.
Or at least it should appear: if there is no Bluetooth device already paired with the Mac, it may remain hidden.
Toggle (off and back on) the MIDI button in the toolbar

In order of "severity" of intervention for Bluetooth problems:

• Remove all devices to reset the pairing settings and start over;
• Restore factory settings to restart from "clean" Mac and peripheral configurations;
• Restore the Bluetooth module.

See also How to solve bluetooth audio problems