When you press a button on the Logitech Harmony Ultimate remote control, the button press is sent over RF to Logitech's Harmony Hub, which in turn can forward it to your Mac via Bluetooth.
A direct Bluetooth connection between the Logitech Harmony Ultimate remote control and your Mac is not possible.
Configuring Harmony Ultimate for Remote Buddy 2Knowledge Base
Resetting Bluetooth How do I set up the Harmony Hub and connect it to your app on my Mac? Nothing happens when I press a button on the Harmony Hub remote. When the Harmony Hub connects to my Mac, I'm asked for a PIN.
RF (Remote to Hub),|
Bluetooth (Hub to Mac)