Magic Keyboard: Function Keys are only working with lightning cable attached?

My magic keyboard works perfectly fine as long as I have the lightning cable attached.

The keyboard overview with the cable attached looks like this:

idk why those two keys are highlighted, but everything works as it should.

As soon as I unplug the cable, the layout changes, the fn key stops working and the the F keys are just F keys and stop brightening my screen etc.

I think it´s weird that the layout changes, as if it would see a different keyboard without the cable...

Of course I tried ticking the "standard function keys" box in the keyboard system settings.

Any suggestions? Anyone else with this problem??

Thanks!

Robin