this is wildly anti-user and turns a preference->behavior mapping of

dark -> dark

light -> light

os preference -> os preference

into

dark -> impossible to know with just this info

light -> impossible to know with just this info

os preference -> impossible to set via the app

if you absolutely have to account for the third case, then you need an explicit option for it and should be able to tell the user what their current os preference is. all the information i need to make a decision should be present in the interface, and the underlying code should do what the fuck i tell it to, not what it thinks i meant.