There is no fix for this as nothing is broken.
Neither the iPad nor the iPhone will "pair" with a Mac using Bluetooth in the traditional sense as you might pair headphones to a device. This is expected behavior as it has never been a feature of these devices.
If you wish to sync these devices, then the connection between i-devices and the Mac must be made with a data cable, either USB to Lightning or USB to USB-C depending on the device.
You can also use iCloud sync between these devices if you sign into iCloud on each and enable the iCloud sync in Settings. You will use your Apple Account/ID to sign in each device. You will use the same Apple Account/ID on all devices.
Set up iCloud Drive on all your devices - Apple Support