The dark mode theming is done (by default) by the constant ‘darkMode’ in /theme/native/custom-variables.js#29 :
// Dark Mode - Inherits OS theme if possible export const darkMode = Appearance.getColorScheme() === "dark";
You can circumvent this by replacing this line with something like this:
// Dark Mode - always off export const darkMode = false;
Thanks for your quick answer, it helped me a lot.