Repeated error message, unable to work in any files, please help!

I have not changed anything including the place where I save and back up my files, but all my files keep closing after I open them and showing this error message:
" .scriv file package could not be located"
It’s preventing me from doing any work. What is this problem and how do I fix it quickly?
Screen Shot 2020-08-03 at 5.51.44 PM.png

EDIT: deleted my original post as Silverdragon’s answer below is far better.

:blush:

It’s not so much Desktop and Documents (tho turning that off won’t hurt.) The real culprit is “Optimise Mac Storage.” Scrivener expects all the components of a Scrivener project to be present on your local drive. “Optimise Mac Storage” will take stuff off your local drive, storing it only in iCloud. To turn off this option:

Open your System Preferences, and click on iCloud (or Apple ID if you’re running Catalina.) Then be sure the box for Optimise Mac Storage is not ticked. (See screenshots below.)

Hope this helps!