I recently write a program in shell script to easily changing a Linux device's brightness. This is because you can't do that in a tty or kterm. It also should be more precise than a gui.
Since it adapts to your system it should run on any kindle with a backlight and the ability to run kterm. Here is the github page:
https://github.com/D2Lx0wse/brightsh...0.1-prerelease
And here is a tutorial for the kindle with a demonstration.
https://youtu.be/pH3maCk90Ok