
If I were you, I will choose the auto downgrade method cause it is much easier.

You can either choose to downgrade kindle app to older version manually or automatically. If you are using the latest version (higher than version 1.17) of Kindle application, please revert to older kindle version. Make sure you’re not using any current version of the kindle application as the kfx format books can’t be unlocked yet. Please follow 100% effective method to remove kindle drm on Mac Catalina and Big Sur. Older Kindle for Mac will not work on Catalina or later Mac OS because Kindle app older version is 32-bit, and Catalina and later Mac os require 64-bit.

If you are running Catalina or Big Sur, you must use K4Mac 1.25+. Download and Transfer via USB Kindle (Last Update 2023) Method 1 - Use Older Version Kindle for PC/Mac(Version 1.17)
