I don't believe iCloud is a filesystem, it's not block-level. It's object-level, like S3, with a bunch of OS-side jank to make it look like a conventional directory and filesystem (which often fails miserably and dangerously).
It's similar levels of reliability to an FTP account mounted with curlftpfs[1] - except the latter at least fails in understandable ways and can be debugged.
That's exactly my mental model of it as well, some janky home made s3 fixed with tape. I really advise anybody to save their data somewhere else as well before in inevitably stops working.
It's similar levels of reliability to an FTP account mounted with curlftpfs[1] - except the latter at least fails in understandable ways and can be debugged.
[1]: https://news.ycombinator.com/item?id=9224