"My MacBook Desktop disappear after update: I bought a new MacBook, started it as normal, used it, logged into my Apple account, and this laptop has it's own independent desktop that wasn't shared with my iMac. It auto updated and I had to log back into my Apple account and it's now replaced the desktop with my iCloud Drive desktop shared with my iMac and the original desktop that was on my Macbook has now disappeared with all the work etc that was on it. How do I get it back?"
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Recovering Data After an Update:
A. New iCloud Session:
Log out of iCloud, and then log back in. You’d do so in system settings. Restart your Mac after the login.
B. Reinstall the macOS:
Go Here: How to Reinstall macOS from macOS Recovery - Apple Support. If the update got a bug, or was unsuccessful, then this would reinstall missing items, and relocate item to where they should be.
C. Restore from a Backup:
Did you create a Time Machine Backup of your Mac prior to this update? If so, restore your Mac from it. If not, then take this as a learning experience, knowing to always brate a TMB prior to making any changes to it, such as an update installation, or format. That way, you can have something to restore it from, shoudl anything go worng after the install.