iPhone SE AirDrop (Bluetooth?) to iMac fails on Sonoma 14.5

I have an iPhone SE from 2017 running iOS 15.8.5 and have until a few weeks ago (when MacOS was updated) been able to pair the phone to my iMac i9 2019 with Airdrop and Bluetooth in order to send photos across to the iMac. (I'm assuming BT is involved in the process) However now the iPhone SE shows the iMac as available but reports it can't pair with it. My iMac doesn't now recognise there is the iphone nearbye so I can't pair from that side either. I have tried restarts on both devices but both still report the same. I'm running OS Sonoma 14.5 as I do not have any spare disc capacity to upgrade at present and need to sort out some legacy software issues first as well as try to make a full backup. I am a bit fearful of the update causing problems. I think I recently updated the iMac version of Sonoma from an earlier one for security updates but I can't remember which version was previously running (May have been 14.1). Could the iMac update have changed Bluetooth/Airdrop compatibility with the SE?

I also notice that although both devices say they are discoverable the System Report details curiously say for the Bluetooth Controller

"Chipset: BCM_4364B0

Discoverable: Off" whereas the software says it is discoverable and I know it works with other BT devices in the house.

I'm not technical and not a computer boff, so need a simple answer to what is to be done

Question: If compatibility has been changed by the Sonoma 14.5 update how can I now transfer photos from the SE to the iMac?

Model Name: iMac

Model Identifier: iMac19,1

Processor Name: 8-Core Intel Core i9

Processor Speed: 3.6 GHz

Number of Processors: 1

Total Number of Cores: 8

L2 Cache (per Core): 256 KB

L3 Cache: 16 MB

Hyper-Threading Technology: Enabled

Memory: 8 GB

System Firmware Version: 2022.100.22.0.0

OS Loader Version: 580~2215

SMC Version (system): 2.46f12