Ctrl and the display brightness keys bind to the keyboard backlight
A MacBook Air M1 (J313) from 2020 sends no keyboard-backlight keys. ludagoo's change merged into quattro, and the same bindings into v4-5-0, bind Ctrl and the display brightness keys to the keyboard backlight, and this pass has not booted it as a new kernel.
F5 and F6 are Dictation and Do Not Disturb, so Ctrl and the display brightness keys are the way to change the keyboard LED. The change binds those keys down and up. The existing keyboard-backlight bindings stay. The change has not been booted as a new kernel in this pass.