Magic keyboard replacement loses Fn keys

Hi,

I've just received my new magic keyboard to replace my old 2013 one, and I was surprised to find that adjusting the brightness/volume was impossible. I checked System Preferences and noticed that the "Use F1, F2, etc. keys as standard function keys" option wasn't there.

From there I unplugged it and replugged my old one to find "Use F1, F2, etc. keys as standard function keys" back and well unticked.

I read that if this option didn't show it meant that my keyboard wasn't Apple-manufactured, which isn't the case since I literally ordered it from Apple directly.

It can't be OS related either since I'm not connecting it through Bluetooth but via lightning cable.

Thank you for helping me out here, I've only managed in retrieving the brightness F1/F2 keys from the shortcuts section. The fast-forward/volume etc options are not showing there, not really keen to use a silent iMac!