I’m assuming this was a Windows error you got? You double-clicked on the .zip file (or opened it in something like 7zip or WinZip) and that is when you got the error box? If you tried to open the .zip directly in Scrivener that wouldn’t work.
That aside, restoring is just a matter of copying the folder out of the zip somewhere and opening it as you would any normal project—and indeed at that point it is a completely normal project. Backups are just that, project folders that have been zipped up to save space and discourage directly editing them.
If there is nothing here for this project, what were you opening before that gave you the “Can not open output file” error?
What happens if you use File/Back Up/Back Up To... and point that at a convenient location like the Desktop. Does a file show up?
Do you mean the tutorial? That would get backed up like a normal project because that is what it is, but the user manual is a PDF that should be loading in your system default PDF viewer, there shouldn’t be any backups of that.
Thanks for the screenshot, that helps. One thing I’d recommend is making a folder just for Scrivener backups, it’s up to you, but considering that it does periodically remove files from this folder, I’d want to keep it in its own playpen. Just to be clear that should be safe. It removes files based on the naming pattern for old backups.
Okay, looking at the size column, it does indeed appear these backups are empty. 14kb is probably the minimum filesize on your system, they are probably in reality much smaller. What I would try doing is turning off the .zip compression option as a test and see if they come through. The tutorial project appears to be a good backup, so it’s probably not a universal problem, but something in your project that is causing either the backup routine or the zip compressor to fail, and switching it off would help us know where that failure is.