Which flutter architecture is more adopted today? Is possible to include it as a library in native applications?

Im about to start a new module in my work project and i was considering to use Flutter, because it's a simple feature but needs to be applied as a library to an existent app (that is built natively in Android and iOS).

So, i have these two questions:

1. The most used architecture nowadays
2. Is it possible to agregate it as a library in an native built app

Thanks!