Newly Published Kindle Files can't be Downloaded via the Older Versions of Kindle Apps

Since Amazon has adopted the KFX format, there’s no DRM Removal tool that can handle Kindle KFX files. Therefore, in order to skip the KFX format, you need to downgrade the Kindle app to an older version to be able to remove Kindle DRM. However, as of today, newly published books seem to be affected. Your Kindle for PC/Mac requires the latest version to download and view the content. Of course, you can still download older books via the older version of Kindle for PC/Mac. 

Luckily, Downloading & transfer via USB targeted to an e-ink Kindle still works even for the newly published ones. 

Here’s a step-by-step guide to help you remove Kindle DRM by downloading Kindle books through Download & transfer via USB method from the Amazon website.

This guide works for both Windows and macOS users. The bad news is that you can't use this method if you don't have a Kindle e-Ink device.