I have created a new project of React Native with a typescript template using the official command react-native init MyApp --template typescript (a couple of times
I have find the solution, and basically when you create the react native app using the typescript template in the ./ of your project apperar 2 files named App (App.js and App.tsx) so basically the solution to get this working is go to the index.js and replace
import App from './App';per importApp from './App.tsx';
index.js
import {AppRegistry} from 'react-native';
import App from './App.tsx';
import {name as appName} from './app.json';
AppRegistry.registerComponent(appName, () => App);
Also you can solve the problem removing the .js file so the index will point to the .ts