[BetterRed]

@Misachat - global Preferences located are wherever you land when you go into Preferences->Miscellaneous and click the Open configuration directory button.

It's location varies according the OS your using. If you want to put it elsewhere, then that can be achieved via the CALIBRE_CONFIG_DIRECTORY environment variable. It isn't a database of such, it's a collection of folders and files containing global preferences, plugins, customisation data etc. You should include it in your backup/restore and disaster recovery considerations.

In the library book folders you should see files named 'metadata.opf'. Copy one of them somewhere (e.g. desktop). Open it with a half decent editor (e.g. Notepad++), replace all the '"' strings with nothing; that will make the file easier for you to read. You should be able to work out your original column definitions by looking at a couple of metadata.opf files.

You didn't tell us why you separated the library database file and the library preferences backup file from the library folder, or how (via the environment variable, symbolic link or otherwise) you did it.

I assume you did a destructive reinstall/reset of Windows 10, and that you didn't take an system image beforehand - that's another lesson to learn.

If you do have a pre-reinstall system image then why don't you restore it, secure the critical data (I would copy the contents of the Users and Program Data folders somewhere safe.) and then do a non-destructive reinstall, in Windows 10 it's done via Settings->Update & security->Recover->Reset this PC

BR