fn keys on external keyboard mac

I would like to have my keyboards set up so that the fn keys on my laptop keyboard are always the macos specific functions i.e. brightness, volume etc.

But on my external magic keyboard the they are F1, F2.... etc which is much more useful for programming.

This was previously possible on my old laptop with a touch bar but now the same checkbox in System Preferences > Keyboard has different wording and does not only apply to external keyboards, it applies to both.

Is there any way to achieve this with the new M1 macbook pros?

I have tried third party software to remap the external keyboard but then I lose use of the fn key and the keys are permanently on F1...F12.