Images in Media Folder not available


I tried to see if there was already a thread on this - couldn’t find one, apologies if I missed it.

So - Attempting to just attach an image to an email on a client’s iMac - but from the Photos App database. This is found by, once having scrolling down to the Media section and selecting Photos.

On my iMac (running High Sierra) there is no issue - the Photo App is displayed and underneath it all of the local and shared folders in the app so I can select whatever image(s) I wish to.

On my client’s iMac (running Mojave) the Photos app is shown, but then nothing else. No folders, no selectable images in the folder contents below.

I first though this might be to do with the iCloud option in Photos where you can ‘Optimise Mac Storage’ which only keeps local low re proxies on your Mac. But the option was set to the opposite - Download Originals to this Mac.

2nd thought is to rebuild the Photos database but yet to have the chance.

Are there any other possibilities?

Thanks for any pointers.

Does no one have any idea?