Mass import a complete library isn't a good solution. Use instead the calibre export/import functionality
https://manual.calibre-ebook.com/faq...ter-to-another
Or, if you like to do it manually, copy the complete library folder to the new place and tell calibre where to find the library. Same for the configuration directory if you want to have your old configuration setup too.
https://manual.calibre-ebook.com/faq...backup-calibre