I bet your mistake is simply that createStackNavigator() shall be apart from any component ;

...
import ScreenOne from "./src/screens/ScreenOne";
import ScreenTwo from "./src/screens/ScreenTwo";


const Stack = createStackNavigator();

export default function App() {
  return (
    <SafeAreaProvider>
...

You might want to take look at the documentation.

Otherwise, you may check out this similar question