Many thanks for the pointer - that's really useful. I'd missed the fact that the photo.metadata["{DNG}"] contained important info like the BlackLevel expected minimum value. Thanks for your help.

Just to confirm that the second approach does work on these devices - although you do have to silence the phone to mute the shutter sound!

Thank you so much for the information. We're unfortunately currently using an iPhone SE (3rd gen) although likely to upgrade to a 16e shortly - so that probably rules out the AppleLog approach. Is the second approach (AVCapturePhotoOutput to take Bayer RAW) likely to work on either or both devices do you know?