Highlighted FN keys turn red (Blackwidow v3 mini hyperspeed)

I have a Huntsman Mini and I just had to hold the FN key and the press the button that looks like a page directly to the right of it, I guess this works as FN lock.

I see your keyboard doesn't have it, so either try every key (shouldn't be a problem since if it's not the wrong key it won't do anything), or look it up specifically for your keyboard model.

Maybe also try FN + CAPS LOCK, that could work.