On April 13th I posted:
"I found a way to workaround the photo sync.
My hardware: MacBook pro Retina 2015, iPhone 6s, iPad pro 9.7" first generation plus my wife's iPhone 11 and iPad Air 2 2014. All of them with the recent OS updates.
Here my way to sync the Photos from my MacBook pro to the iPhones and iPads:
1st unselect Photos in the iCloud settings of all devices
2nd connect the iPhone/iPad via lightning cable with the Mac
3rd make a backup of the iPhone/iPad
4th in the Finder select all contents but photos to be synced
5th select the photos to be synced from the folder of the Mac (in my case the path is users/shared/data/photos1, photos2, photos 3. Each of these photos folders has several subfolders from 50 to 500.)
Important: Stay on the Photos page of the sync tool!
6th click on "apply".
7th if there is an error message like "folder 'unknown' not found" select the folder on the Mac again and click on "apply" or "sync", whatever is offered.
8th if it is still not syncing or even deleting your photos from the iPhone/iPad repeat step 7th.
This worked for all my devices. The only problem: I have to run one more sync for the music.
Next I tried it with my new iPad pro 11" 2020 and it's working as well.
Next experiments I did: Syncing with Win 10 based iTunes.
I tried it using BootCamp, but unfortunately this doesn't give acces to the Mac partition.
Next I tried Win10 with Parallels on my Mac. This doesn't work as well. iTunes crashes after some minutes.
Perhaps I will try Win 10 with VMWare and Virtual Box as well.
Finally I want to say, that Apple was an excellent example for reliable Hardware and software as well. This was their big advantage over the competitors and this was the reason for the relatively high prices they could charge from the customers."