Calling into Unity from Android app?

I am researching how best to write an app. A requirement is that the 3D game engine is not loaded first thing, and assets and API communication are handled in Android/Kotlin code. The game will be just one Activity in the app. Scripts and assets must be handed off from the app to the game engine at runtime, and some in-game events must call app methods. Is there an example of how to do this with Unity, or is this use case not supported by Unity?

 

Unity isn't a library you can just add to a non-Unity project.

 

Thanks Joe. There is more than one way to embed a game engine, but anyway, that sounds like a definitive "it's not supported." I appreciate the answer. Sorry I don't get to use Unity, though.