No, Flows created on iOS will not work for Android and vice-versa. Any in-app content created on Android needs to be created separately for iOS as well.
This is because there are differences in apps on Android and iOS, especially with respect to how the app screen is structured. Element selection is separate for any in-app experience.
Additionally, the in-app experience for a certain framework is optimized for it. This helps in streamlining the content files that reach your mobile app.