iCloud photo mismatch, debug options? I use iCloud photos, on a new Catalina MBP and on iOS 13.6.
on both of those devices I see 7201 photos.
yet, on iCloud.com I see 7200.
there is always a one photo difference.
Adding and removing photos made no difference, iCloud and the Apple devices just gain and lose photos normally. Yet the difference is always there.
Any ideas how to debug?
On your Mac, create a Smart Group with the filter:
Photo | is | unable to upload to iCloud Photo Library

This should hopefully display the problematic photo, which you can try to delete and re-add.
https://daringfireball.net/linked/2018/01/26/apple-photos-unable-to-upload