Disable KFX support in Kindle for PC/Mac
As an alternative, a method is available to prevent versions 1.19 through 1.23.1 from making use of KFX format. Exit the Kindle program. Open a command window (PC) or terminal window (Mac). Cut and paste the appropriate command for your operating system to disable the renderer-test program.
PC:
ren %localappdata%\Amazon\Kindle\application\renderer-test.exe renderer-test.xxx