Photos and Contacts no longer download from iCloud

Since Mid July 2025 all Photos and Contacts no longer download to the iMac.

I have been in contact with Apple support for over 2 hours, verified all the settings (on iPhone and iMac) and they could not provide a solution, the only suggestion was that my Mac is not too old! (10.13.6 High Sierra) But everything was working fine till mid July. Calendar, Mail, Notes etc. are still corresponding with iCloud, i.e. any changes made on the iPhone (16) are immediately updated on the iMac, only Photos taken, or the entire Contacts list is not returned from iCloud.

I am at wits end and hope to find a solution in this community.

Thank you in advance.

Didier