Screen size to design for Android and iOS React Native App?

I am designing a mobile app (UI/UX Design) for a client that will be developed using React Native. What screen size should I start with? Do I need to design 2 different apps for this?

I have been designing single platform apps up till now and I know how the screen sizes work. So I know what the base screen size for Android (width-360px) and iOS (width-375px).