// Old
ReactDOM.render(<App />, container, () => console.log("renderered"));

// New
const App = ({ callback }) => {
  return (
    <div ref={callback}>
      <h1>Hello World</h1>
    </div>
  );
}
const root = ReactDOM.createRoot(container);

root.render(<App callback={() => console.log("renderered")} />);