Anyone find a way to have the keyboard backlight controls work for the keypad also? I know you can use the enter key with num lock off but thought it would just be a nice option to control both at once.
You can do it, but it will require compiling firmware, and you’ll have to be able to write some code.
Basically this is correct.
Is this a linux specific issue? i.e. if someone had the numpad module installed and windows as an OS, does fn + {Spacebar} simultaneously control the numpad brightness?
It’s not a linux issue. Hotkeys such as Fn+Space are independent from the OS. It’s handled entirely within the keyboard itself. But the keyboard does not pass commands to other modules, such as a numpad or macropad. At least the default firmware doesn’t. Standard USB HID devices such as keyboards don’t have a proper way to do it without involving the OS. As I mentioned, there is a slightly hacky way to accomplish it in qmk, but it requires compiling firmware, and being able to write some code.