Keychron mechanical keyboards are pretty nice and not too expensive. Unfortunately, out of the box, when in Windows-mode (rather than IOS-mode) the function keys to not work for love or money (not even if you press the [fn] key.)
The answer to this problem is that since IOS is at its essence Linux, you tell Linux to treat the keyboard as an IOS keyboard while telling the keyboard to behave like a Windows keyboard.
This answer comes from Bastian Venthur who gleaned it from the Keychron Linux users.
Create a line in a file called /etc/modprobe.d/hid_apple.conf with one line in it options hid_apple fnmode=2
I think this tells Linux to treat the keyboard like an Apple keyboard.
Then tell the system to reset its initialization:
sudo update-initramfs -u -k all
