I found the problem and cant remember what exercises it was.
But ReactDOM.render = (<ul>{peopleLIs}</ul>, document.getElementById('app'))
Was wrong, it should be ReactDOM.render(<ul>{peopleLIs}</ul>, document.getElementById('app'))
I knew you would spot it on a closer look. We lose focus when looking at something too long. Taking a break and returning later gives us a fresh set of eyes. Good that you spotted your error!