There is no public/index.html to start the app

[hisandan]

After npm start Index.js search for the 'root' div, with the following command: document.getElementById('root')

This element have to be in public/index.html file or the app will not run.

[hisandan]

It is also necessary to use in index.html:

const root = ReactDOM.createRoot(document.getElementById("root")); root.render( <React.StrictMode> <App /> </React.StrictMode> );

instead of

ReactDOM.render( <React.StrictMode> <App /> </React.StrictMode>, document.getElementById('root') );

because the last is no longer supported