Pairing iPad Pro 10.5 with IPhone 12

Correct, this is expected behaviour. While there are many activities that require Bluetooth to be active on both devices, those activities will not require pairing in the traditional sense. What are you hoping to accomplish?

Everything that you do on the iPad or iPhone will be updated if you have enabled Calendars on iCloud for both devices.

More info here:

Set up iCloud for Calendar on all your devices - Apple SupportAppleOfficial Apple Support › guide › icloud › icloud