FN Brightness for Up and Down has been changed at High Sierra and Mojave. But i don't know how to compile the source code from Mojave.
See this : https://github.com/RehabMan/OS-X-Voodoo-PS2-Controller/blob/master/VoodooPS2Keyboard/ApplePS2ToADBMap.h
We need to apply like my screenshot, not 0x6B and 0x71 anymore