My iMac is now fully restored. Hundreds of files started disappearing in many folders. I restored a few missing files and they disappeared again in the next few hours. These spontaneous mass deletions were happening for 2 days before I noticed it. An anti-virus program said no viruses. An apple rep and a friend who repairs Apple computers said beware of problems stemming from the use of iCloud Drive. I am using auto-update on OS, but the latest (Ventura 13.2) hadn't kicked in yet..

Bottom line is that I am perfectly good now and the problem has stopped. I rotate 3 separate external drives for my backups. I also put all of my data into Dropbox Professional which has an excellent "rewind" feature that comes with diagnostic charts that let you see where and when activity is happening, also allowing selective or global restore. To make sure there were no remaining vestiges of the problem, I ended up tearing down my machine to bare metal and building it back with brand new OS, manually updating the most recent safe-seeming backup, then restoring 2.5TB of data. Then the tedious task of installing and configuring a dozen apps. I also disabled iCloud Drive. Take-aways: A) Big problems can occasionally happen even with an Apple computer. B) This was a major problem and I was prepared with ample backups, C) Dropbox Professional is worth every penny, and D) Constantly back up your computer with Time Machine, an incredibly sophisticated and easy to use program!