Maybe this is obvious but I thought it was a bug at first! The Bluetooth “Discoverable” button doesn’t work (and provides no feedback), if there is already a bluetooth device connected. You have to first disconnect the current connected device, and then you can turn on Discoverable.
And I guess- enhancement request- make the Discoverable button disconnect the current device. Or gray out the discoverable button if there’s a device connected. The way it is now is a bit confusing- you can press the button but it just doesn’t work!