photos library on mac doesn't sync correctly to icloud

My library of 48,000 photos and 1500 videos are carefully organized on my mac in the photos app (and backed up with Time Machine). However, when I turn on iCloud and try to synchronize this library, the folder structure I started with is not copied correctly to iCloud. Furthermore, in the process of syncing, my library on the mac is also corrupted and mirrors the errors from iCloud.

My original library is not very complex or complicated, mostly just folders with albums sorted by year.

I have tried repairing the library using the in-built tool. I have restored the original library several times. I have deleted the iCloud version of the library and started fresh. I have disconnected all devices from iCloud just to be sure there are no other conflicting inputs.

Any ideas why this is happening and is there a way to enable iCloud without ruining my library?