[Cootey]

For Mac owners running Catalina or higher, here's a method to prevent the app from updating.

1) Put a clean copy of Kindle 1.31.0 in a folder on your desktop. Label the folder something useful like "KindleCage"
2) Open Terminal.app and run "sudo chmod -x ~/Desktop/KindleCage/Kindle.app/Contents/MacOS/renderer-test" just for good measure (all one line!). This prevents renderer-test from executing. Adjust your path as necessary.
3) Open "Disk Utility.app". It's in /Applications/Utilities.
4) In Disk Utility's menu, select File>New Image>Image from Folder. Then select the folder that you created in step 1.
5) Choose a name and destination for your disk image. This creates a read-only disk image. "KindleCage.dmg", for example.
6) Open the disk image. Holding down option+command, drag the Kindle icon from your disk image to your preferred location. You are creating an alias, so there should be an arrow now part of the icon at the bottom left.
7) Delete any instances of Kindle.app on your Mac. Amazon will find them, update them, then try to run from the update.

From now on, double clicking on the alias will automatically open the disk image and run Kindle.app from there.

If this is repeat information, I apologize. I didn't see it mentioned in my search.