<div class="container"></div>

const useState = React.useState

const App = () => {
  const [visible, setVisible] = useState(false);
  return (
    <>
      <button onClick={() => setVisible(true)}>表示</button>
      {visible && (
        <div
          style={{ border: 'solid' }}
          tabIndex={0}
          ref={(e) => e?.focus()}
          onBlur={() => setVisible(false)}
        >
          表示内容
        </div>
      )}
    </>
  );
};

ReactDOM.render(<App />, document.querySelector(".container"));