Interesting. I wonder if I am encountering a similar issue migrating to a new MacBook Pro, where the iCloud Library contains over 18,000 files.
viewtopic.php?t=6092
I'd appreciate if if anyone with technical expertise resolving this issue could cast an eye on that thread.
(I also found that Bookends IOS became unusable because the Files app was failing to update, so I was interested to read this - however one issue at a time!)
Malcolm