Just finished 2 hours on the phone with Apple Support. The last support specialist insisted that there were only a few users impacted by this issue (there are more than a few).
I also have the 2TB plan, really just for photos. Maybe it is anyone that has the 2TB plan that is experiencing this issue when upgrading to Sonoma.
All of the error prompts in iPhoto are incorrect or dead-ends. And the iCloud prompts to solve put you in a circle.
And it is not easily resolved. muguy is what I started with. But then I had to download my entire iCloud photo library down onto my Mac (it is big) and use that to get iPhoto on the Mac functioning (partially) again. The past several weeks of photos are missing on my Mac, but hopefully that resolves over the next several hours.
If the product manager is monitoring feedback, please...next time there is an OS upgrade, invest in doing UAT instead of just basic regression testing. This is not an edge case scenario (all photos disappearing from a Mac). I do not like to use the word 'glitchy', but this iCloud/iPhoto Mac issue exposed several glitches (random reboots, unable to shutdown, having to use safe mode) while getting iCloud/iPhoto resolved.