Ok, apparently, for iOS, I need to use the themeVariant , otherwise, if my phone is on dark mode the picker will use the colour scheme expected for dark and although I've styled my items with text color, it didn't assume it.
On @react-native-community/datetimepicker I can just use themeVariant but on "@react-native-picker/picker": "2.11.1" I will need to use PickerIOS if I want to control the theme variant