I did the following with Kindle PC version 1.24.x and was able to successfully convert the new .KFX Kindle book files to .Epub using DeDRM.
1. Install Calibre
2. Install KFX Input and Output plugins separately using the "Get new plugins" option in the Plugins section. Search for KFX, you should find an input and output plugin. Install them both.
3. Install the 3rd party DeDRM plugin file as instructed using "Load plugin from file" option in the plugin section. Get the DeDRM plugin from
https://github.com/apprenticeharper/...tools/releases
Hopefully this works for you'll. Thanks!