Welcome to the forum.
We must be careful with the terminology.
Bluetooth Classic and BLE are two incompatible protocols that only share the name and the frequency band (2.4GHz). The Arduino Nano 33 BLE is a BLE only device. It does not support Bluetooth Classic.
I suspect your Firefly uses Bluetooth Classic with the Serial Port Profile. BLE does not support SPP because it is not energy friendly and a bit outdated.
Pairing is an optional feature in BLE. Paring is usually done through the mobile operating system and requires the user to confirm the process via some pin code. The ArduinoBLE library does not support pairing. BLE devices can just connect. Connecting can be done from within the app.
There are modules that support Serial over Bluetooth Classic with little configuration. You should investigate which module would be compatible with your adapter. There are a few people in the forum that have knowledge about these modules. You may want to provide some more detailed information about the Firefly adapter to help them help you. e.g., link to datasheet or other useful information.