Problems sideloading images with Calibre after latest firmware - kindle read-only

[Celegit]

Good evening, everyone,

I would need help with a problem that has occurred since I upgraded my kindle to the latest available firmware. It concerns the thumbnails of files uploaded through Calibre.

Before the update, if I restarted the computer and my Kindle Oasis 3 (the device I have), Calibre was able to transfer AZW3 files to the kindle including cover images (thumbnails). Since the update, if I load them through Calibre, the cover images are no longer loaded into the 'Thumbnails' folder, which is a subfolder of 'System'.

I noticed that the Kindle is recognised by Windows 11 Pro, my operating system, as a 'Read Only' device. I've tried changing permissions, giving it full control, but nothing changes. Calibre only loads the AZW3 file, without being able to access either the Thumbnail folder, or Amazon_Folder_bug, which was the workaround normally used by Calibre. I can't even try to paste the jpg thumbnail files into it.

Restarting the Kindle and PC did not help any more.

I know that it is possible to send one's books by email to kindle, but as I have changed the layout of the books, I have noticed that if I send them, while retaining the images, all my layout settings in the file are reset to the default settings and the epub file converted to kfx.

Is there any way to make calibre able to upload the thumbnail and write the image file to Kindle again, so that I can retain the page settings for my books?

THanks a lot,

C.