Lost files

Do you have iCloud desktop and documents enabled?

Go to the Apple Menu > system preferences > iCloud and review your settings

This support doc may help: https://support.apple.com/en-us/HT206985

If you know the name of a file, you should be able to search for it and find it.

Also, take a look at your iCloud folder in the finder sidebar.

Finally, check in your home directory.

Look & see if iCloud Drive got enabled.

Safe Boot, (holding Shift key down at startup), does the problem occur in Safe Mode? Could take 10 minutes.

Safe mode attempts to repair Disks & clears lots of caches & loads safe Drivers, & prevents loading of 3rd party extensions, so if Safe Mode works try again in regular boot.