@oren b ,
I understand your feelings.
Currently, I suggest you go to folder /Library/SystemMigration/History/Migration-UUID/QuarantineRoot/
, check whether you can find these files.
If it does not work, in addition to using iCloud, have you synced files to OneDrive?
If yes, you may search these files on OneDrive, then you may download files to your device.
Besides, do you have Time Machine backups?
If yes, I suggest you use Time Machine to restore the previous save.
Before upgrading macOS, it's best make a backup of your Mac, in case the changes bring something unexpected like data loss.
As this issue maybe related to system update, I also suggest you post a new question on Apple community.
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