react Switch is no longer supported in React 18

<Switch>  
  <Route path="/login"><Login /></Route>  
  <Route path="/"><App /></Route>  
</Switch>

아래와같이 고치면 된다.

<Routes>
  <Route path="/login" element={<Login />} />
  <Route path="/" element={<App />} />
</Routes>

핵심은 
1. Switch -> Routes
2. element={<Login />}
done.