Unless React Native and similar, Flutter use their own widgets instead OEM native widgets, and use the mobile platform channels to access the services of the devices. Thus, Flutter manages to operate completely natively in both Android and iOS avoiding the use of JavaScript, external bridges, and performance funnels.
The functionality and structure of this software allows the development of flexible, custom and scalable apps, making the implementation of already created and built-in code easy and compatible with all Android and iOS devices and OS versions.