The latest generation, Kindle Paperwhite, Kindle Scribe 2, Kindle Scribe 1, and Kindle and the upcoming Kindle Colorsoft, all have something in common. When you plug them into USB into your PC or MAC, they no longer appear as external drives. This prevents users from using file managers to back up their books or to sideload new books onto the Kindle. Amazon has also removed the download and transfer via USB option for purchased ebooks from the content page. This will likely prevent people from striping the DRM from the books and sharing them on piracy websites. This is not
Pretty minor as long as your computer’s OS supports MTP, which most do, except for MacOS. If you’re a Mac user, you’ll need 3rd party software like Calibre or Android File Transfer for it to show up, but if you’re the kind of person who’s transferring books to and from your Kindle over USB, you’re probably already using Calibre anyway.