const About = ({ isAuthMounted }) => {
  if (isAuthMounted) {
    // ...
  }
};

const Auth = ({ setAuthMounted }) => {
  useEffect(() => [setAuthMounted(true), () => setAuthMounted(false)], [setAuthMounted]);
};

const Parent = () => {
  const [isAuthMounted, setAuthMounted] = useState(false);
  return (
    <>
      <Route path="/about" component={About} {...{ isAuthMounted }} />
      <Route path="/auth" component={Auth} {...{ setAuthMounted }} />
    </>
  );
};