Recently i bought a zuoya gmk67 keyboard, it doesn't have a function keys row and has a knob for volume control. Unfortunately, if you plug your gmk67 in a archlinux machine you will notice that using fn+1 will not produce f1 as expected, it will produce a screen brightness decrease, and if you change the physical switch in the back for the macOS mode, the function keys now work, but the modifier keys don't, quite stressful.
Fear not, you can either alter your system configuration so the keyboard functions normally, as in this gist, or remap the keys, as seen in the gist Using GMK67 keyboard in linux with key remaps!.
For this gist we are going to alter the configuration for the apple hid driver on archlinux, since this keyboard uses it, and alter the functionality of the Fn key.
This is tested on archlinux, for any other distro you might have to figure out yourself the correponding commands!