GUI is something like an API, let's take React Native - you just have an api to rendering (via bridge), same for X server, same for almost any GUI framework. T

GUI is something like an API, let's take React Native - you just have an api to rendering (via bridge), same for X server, same for almost any GUI framework. This is a very very tiny part of an app. UI libraries with prebuilt controls are already almost always bundled with apps.