Why is iCloud drive so buggy and unstable?

I originally wanted to move away from Dropbox and finally save some money. I have the AppleOne subscription, so with 2TB+ that should have been no problem. But even on a new and clean MacBookPro (2023) after setting up iCloud Drive and sync (everything to disk, not optimising storage), I just get errors over errors. Very generic errors. Reboots don't help, iCloud says it's in full sync, but moving folders or files, or copying data out of iCloud drive doesn't work properly. My MBP has enough disk space and still 300+GB available. The same behaviour shows up on 3 other macs that I'm using, so it's not working on multiple devices. This device just came in brand new!!!

One example is here, while trying to copy a folder from iCloud drive to another local folder:

"The finder can't complete the operation because some data in '' can't be read or written." (Error Code -36)

Well Apple, what do I care? The data is in your cloud, so if you can't read or write it, go and get it from somewhere. This is by far, the worst implementation of a cloud file storage that I have ever used.

Another one, trying to download a newer folder from cloud to disk:

Well, what should I say, my Internet uplink is fine and everything else works. I'm not behind some fancy firewall or weird WAN uplink, it's basic home Internet and it's consistent behaviour at other locations and other WAN uplinks.