I don’t have another Apple device to test it on.
Yes, the create an empty library worked to at least get the Mac in sync initially.
The library would still do its attempt to upload all 22,000 photos even ones that hadn’t been touched in years. I don’t know why Apple does it this way. To my way of thinking they. Should download the new photos first and matching on metadata, file size, and date and only when they differ upload the newer (edited or imported) photo.
I have no idea but 1,400 really old photos were loaded into my phone as recent. They obviously came from iCloud downloaded to the izohone. Now Photos Mac nags me to import what would be duplicates.
I have no idea how to fix that. This happened during an early beta for iOS 13.
Now in Catalina 6 we had a bug that it seemed to hang Photos Mac when I tried to set the empty library as the system library.
Beta 7 fixed that bug but introduced a new one. The empty photo library will not download from iCloud. Add one new photo via import will start the updating … but nothing actually happens. (one of my many persistent whines is that the update function should tell the user what it is doing. At the moment it does not. IOS version gives verbose progress reports.