What problems will I face if I develop an application on a cross-platform framework?

Question

Mobile development

What problems will I face if I develop a mobile application on a cross-platform framework, and not on a native one? For example Kivy, React Native, Xamarin, Unity3D . I know that Unity is a game engine, but it doesn't hurt to create applications on it if its capabilities are enough? I just know Unity, but I don’t want to learn a new technology (or two new technologies, if we are talking about a native).

Answer 1

from just one: all platforms are different
from what works on one it does not follow that in the same layout it will work on another