So you are fucking annoyed by the buttons backlight.
It is too bright, and turns off if you don’t touch buttons and then turns back on when you touch it, and this flickering is exceptionally annoying when you are scrolling a book with volume buttons, and the light flickers right in your face. Generally, brightness level is controlled by these two settings, one of which is set to 0 and the other to 255. But there is an easier way, GravityBox. Download it, install, and run to get an error. Well, download Xposed Installer, then get Framework, and then run GravityBox. Error again. Go to Xposed Installer, then Modules, tick GravityBox, reboot and finally it works. If GravityBox is not in the modules, reinstall it. Generally, correct installation order will be Xposed installer, then Framework, and then GravityBox. Once inside, go to Display tweaks. Here you can switch button behaviour between default, always on when screen is active and always off. I chose always off to save battery. Here is another interesting tweak, still experimental. Button light notification. If your device doesn’t have a notification light, or it is too dark, or its location is weird, but you have backlit buttons in front you can use them for notifications about messages or missed calls. Try it out, this one is really good.