Finder not recognising iPhone12 mini

Morning Folks,

Having a sudden problem with my iPhone. Finder is not recognising its existence (ie no (total) backups, and no manipulation of the photos and music etc.

What I know:

Both my iMac and phone are running the latest available software

It is not the physical connection because photos is automaticaly launching and DOES recognise the phone.

My sons iPhone8 connects fine.

What I have tried so far:

Relaunching both the iMac and the phone.

Any ideas?

Many thanks,

David.