after system update, files on desktop disappeared. I have iMac Ventura

Have your Documents folder also disappeared? Check the System/Apple ID/iCloud settings pane and see if the iCloud Drive is enabled. If it is click on it to see if the Desktop and Documents option is also enabled?

Sometimes during upgrades it gets turned on for some reason.

reel78 wrote:

After system update, files on desktop and in numbers disappreared. I have iMac with ventura

On a Finder window sidebar, click on iCloud Drive. Is there a Desktop folder inside?

If that is the case, it means you, perhaps not realizing it, accepted "Documents & Desktop in iCloud".