icloud photos - desktop library no longer syncing
I had a n issue which meant that I had to turn off iCloud on my desktop Mac. At the time I selecetd to keep local copies of items, including my photos. All fixed and iCloud is back on and 'photos' is ticked in the main iCloud preferences.
In my desktop Photos preferences the iCloud photos is turned off. I guess as a byproduct of turning off iCloud in fixing the earlier issue. If I try to tick it says that syncing the library may exceed the iCloud storage capacity. If I proceed with my existing plan I get the error message attached - this has been the case over the last week or so.
Not wanting to lose the later images in my iCloud photo library, I am not sure how to proceed.
Help please.
Mac mini 2018 or later