The 'Export thing'
is just an easy way to get everything (It grabs EVERY Library Calibre knows about (on the Switch menu) and the settings folder (all plugins and their settings).
The old way was copy the Library folder AND copy the Configuration folder and replace the ones on a FRESH (no books) app install.
No available formats can be from different things.
The Simplest is CASE of the filename (Linux or Mac).
Test: Select a Problem book in Calibre: Tap "O" There should be at least 3 files (There will be more if other formats are there):cover, opf and a format. Icons may vary.
If you see the
missing format or cover. Then this might be a 'case' issue.
Corruption caused by using Google Drive as an intermediary in the copy process (GD fiddles with the (##) part of the name. That is the {id}used in calibre.
The files are really lost because you accidentally put the new Library in a folder that is part of a cloud sync (I think MS defaults 'Documents' to their (OneDrive?) sync.