The thing that confuses me about those nail polishes is like, anyone who uses nail polish to the point where they'd consider that would also be using a clear top coat, which seals the nail and would prevent the conductive nail polish from doing it's "thing"

...also it wouldn't work on most devices because most screens are capacitive, not resistive. Like you can use the backside of your nail on your screen with normal nail polish on and it'll work, because it's about the surface area and capacitive difference, not about closing a circuit