what you used is someones blog. not written by calibre author. it may not be correct.
the official how-to is here
https://manual.calibre-ebook.com/faq...ter-to-another
you could examine that for differences or wait for someone more familiar with the process to assist
it is good that you have the backup file- it should be fixable
FYI metadata is stored in a file called metadata.db in the library folder. If something e.g. security or antivirus is somehow blocking that, you will see the library reported as " empty"
PS when you say "collections"- what exactly do you mean - calibre does not use that term. it has tags, genres, series,,, not collections