To get the function keys to work on the mac keychron keyboard you need to:

• set the switch on the keyboard to ‘windows’
• hold fn+X+L for 4 seconds to enable ‘function’ mode
• setup the hid_apple module by setting “options hid_apple fnmode=0” in /etc/modprobe.d/hid_apple.conf
• if you don’t want to reboot you can set the value using: echo 0 > /sys/module/hid_apple/parameters/fnmode

Then the media keys should work, the function keys will be functions etc.