All books have vanished from Books on Mac Ventura

Dear all

I recently imported a series of books, all in epub format. [iMac 27, Ventura]

I just finished reading one and quit Books and other apps while I made lunch. An hour later, re-opened the Books app to read the next volume in the series – but all I see is a a blank window - where a couple of hours before there were a several hundred titles listed.

Searched the internal and external drives [I have >30Tb of storage] and found several folders [previous libraries, backups etc] but the most recent folder is

Users / Shared / BOOKS

…which contains the titles I imported earlier in the week.

But how do I reconnect them all with the app?

Do I have to import 500 books one at a time?

Move this folder to another location where the app will find it?

Copy the files to a specific location in my named user folder rather than Shared?

OR

SIt in the corner of a dark room with a bottle of wine and forget the whole idea of reading books?

Bewildered

Ken