[Mingyar]

I haven't read the whole forum, so I hope I'm not duplicating anything.
I wanted to share, with those who have difficulties, my method to load thousands of books on a Kobo.
All this text has been translated from French to English by Deepl.

I have a Kobo Aura One LE with more than 13,000 books.
I bought a Kobo Sage on which I went back to the patched 4.30 firmware, after some problems with the 4.31.

I use Windows and Calibre in its latest version to manage my books, in association with the KoboTouchExtended and KoboUtilities plugins.

I got the reading status of the books on the Aura One LE with the Store Bookmarks option in KoboUtilities.

Now, let's tackle filling the Kobo Sage with about 13,000 books.
It's a multi-day operation, tedious, but successful if you're patient and thorough.

The transfers are done in blocks of 250 to 300 books maximum.
For each block:

1. Note the number of books (X) on the reader, displayed on the home screen.
2. In Calibre, send the block of books to the Kobo, transformation on the fly into kepub with the KoboTouchExtended plugin.
3. Upload covers from the KoboUtilities plugin with black & white and keep ratio checked. (this to minimize the space occupied by the covers)
4. Eject the reader AND close Calibre, after noting the number of books transferred (Y)
5. The Kobo scans and recovers the information of the new books. Several situations can occur
   1. After the scan, the home screen displays the right number of books (X + Y). All is well, we go to step 7)
   2. The home screen appears, but the number of books recognized by the reader is less than X + Y, go to step 6)
   3. The scan progress gets stuck on a percentage that does not progress anymore. Give the Kobo a chance for 1 to 2 minutes, then turn it off by pressing the physical button for about 10 seconds.
      After turning the Kobo back on, if the number of books = X + Y then go to step 7) (this is rare) otherwise, go to step 6)
   4. The Kobo restarts by itself, even before starting the scan. Let it restart and wait for one minute to see if it starts the scan.
      If yes, go back to 5.1 or 5.2 or 5.3. If not, go to step 6)
6. The Kobo did not scan all the books transferred (number of books displayed on the home screen < X + Y)
   After making sure that Calibre is not launched, connect the Kobo to the PC, after a few seconds, eject it, without doing anything on it.
   Go back to one of the steps 5)
7. Connect the Kobo to the PC, launch Calibre and select the books of the last block transferred.
8. Update metadata in device library of the KoboUtilities plugin. I check only Title, Author, Series & index, Language and Update Kobo epub.
9. If block contains books with read status and progression, select only these books and restore bookmarks with KoboUtilities plugin.
10. Eject the Kobo.

Repeat all these steps for each block of books.

Again, this method is really tedious, but effective. You can increase the size of the blocks, it's up to you to experiment. Personally, I think that blocks of more than 500 books will cause problems.

This post is an opportunity to thank the authors of KoboTouchExtended (jgoguen) and KoboUtilities (davidfor)

Translated with www.DeepL.com/Translator (free version)