Meteor react mounter and flow router error : Nothing was returned from render

Iam new in meteor + react.

I use ostrio:flow-router-extra

in imports/ui/App.tsx

import React from 'react'

interface Props {
  content?: JSX.Element;

const App = ({ content }: Props) => {
  return content

export default App

in client/routes.tsx

import React from 'react'
import { FlowRouter } from 'meteor/ostrio:flow-router-extra';
import { mount } from 'react-mounter'

import App from '../imports/ui/App'
import HomePage from '../imports/ui/Home'
import AboutPage from '../imports/ui/About'

FlowRouter.route('/', {
  name: 'Home',
    mount( App, {
      content: <HomePage />

FlowRouter.route('/about', {
  name: 'About',
    mount( App, {
      content: <AboutPage />

and last client/main.tsx

import React from 'react';
import { Meteor } from 'meteor/meteor';
import { render } from 'react-dom';
import App from '/imports/ui/App'

Meteor.startup(() => {
  render(<App />, document.getElementById('root'));

I Just follow this tutorial
meteor react flow router

and I dont know where I wrong?

how to solve this? so I can run flow router? or should I change to react router?

additional, ostrio:flow-router-extra still error in typescript lint.