const writeMessage = (msg) => {
  setChat((prevState) => [...prevState, msg]);
}

const writeMessage = (msg) => {
   //newChat = chat.concat(msg);
   //newChat = [...chat, msg]; this two takes inital State, but doesn not work with modified state
   //setChat(newChat);
   setChat(chat.push(newChat)); //this mutates :( and works, but does not re-render itself
  }