ReactJS and Google Maps - Displaying Markers

I'm React newbie so maybe asking a stupid question, but this has got me perplexed. As part of my learning I'm building a three component application - a parent About, and two children (GoogleMap and MapMarkerDetails). The parent does the data coordination and one child shows a google map with two markers as default, the other child shows details of the markers when it is clicked.

I am now adding functionality to add a new marker when the map is clicked. Most of the functionality works - the maps is draw, the default markers are added, and when one of the markers is clicked, this calls a function on the parent class which updates its state and this is propagated to the MapMarkerDetails element and a simple message is displayed.

Here is the parent class which I have commented to help understanding:

import React, { Component } from 'react';
import GoogleMap from './GoogleMap'
import MapMarkerDetails from './MapMarkerDetails'

class About extends Component {

state = {
    markers: [{
        position: { lat: 51.438759, lng: -2.864514 },
        label: 'A',
        map: null,
    }, {
        position: { lat: 51.433636, lng: -2.868734 },
        label: 'B',
        map: null,
    }],
    greeting: 'HelloA'
}

showMarkerInfo = (label) => {
    this.setState({greeting: ('Hello ' + label)})
}

/* 
Adding a new Marker 
This function is called from the child element GoogleMap
However, the setState(...) dosn't seem to propogate down to the GoogleMap element.
*/
addMarker = (latlng) => {
    let newMarker = [{
        position: { lat: latlng.lat(), lng: latlng.lng() },
        label: 'New',
        map: null,
    }];

    /* Creates a new array for updating state. Is this the best way to do this */
    let markers = [...this.state.markers, ...newMarker] 
    this.setState({markers});

    console.log(this.state) // This shows the added marker
}

render() {
    return (
        <div className="container">
            <h4 className="center">About</h4>
            <MapMarkerDetails details={this.state.greeting}/>
            <GoogleMap markers={this.state.markers} clickedMarker={this.showMarkerInfo} addMarker={this.addMarker}/>
        </div>
    )
    }
}

export default About;

Here is the class that displays Google Map and the markers:

import React, { Component } from 'react';

class GoogleMap extends Component {
  constructor(props) {
    super(props);
    this.googleMapRef = React.createRef(); // Create a referance for Google Map to draw to
    console.log('Constructore')
  }

  componentDidMount(){
    console.log('componentDidMount')
    /* Create the Map */
    let googleMap = new window.google.maps.Map(this.googleMapRef.current, {
      zoom: 15,
      center: {
        lat: 51.436411,
        lng: -2.861980,
      },
      disableDefaultUI: true,
    })

    this.placeMMarkers(googleMap) // Place the markers
    this.addMapListner(googleMap) // Define a click listener to place new markers
  }

  /* Place the markers */
  placeMMarkers = (googleMap) => {
    this.props.markers.forEach((m) => {
      m.map = googleMap;
       let marker= new window.google.maps.Marker(m)
       marker.addListener('click', () => { this.props.clickedMarker(m.label); });
     }
   );
 }

 /* Map listeners */
  addMapListner = (googleMap) => {
    googleMap.addListener('click', (e) => {
      this.props.addMarker(e.latLng)
    })
  }

  render() {
    console.log('render: ' + this.props.markers) // This is showing the added markers
    return (
      <div
        id="google-map"
        ref={this.googleMapRef}
        style={{ width: '800px', height: '400px', float: 'left' }}>
      </div>
    )
  }
}

export default GoogleMap

I've added console logging to each function so I can follow what is happening.

Here is the MapMarkerDetails which displays a simple message when an marker is clicked. This all works fine.

import React, { Component } from 'react';

class MapMarkerDetails extends Component {

    render(){
        return (
            <div style={{width: '100px', height: '400px', backgroundColor: 'gray', float: 'left'}}>
                {this.props.details}
            </div>
        )
    }
}

export default MapMarkerDetails

Description of the Problem

When the user clicks on the map (not a marker) this invokes the function addMarker which is passed down from the parent About class (snippet below). In the addMarker function of About the lat/lng is passed in. This represents where the user clicked. This is converted into a marker data object, then a new array is created which contains the default markers and the new one. I'm not sure if my new array creation is done in the best way - if not let me know.

Once the new array is created, we update the components state with this.setState({markers}). I thought this would lead to a re-render() and an redrawing of the map with the added marker. But not.

addMarker = (latlng) => {
    let newMarker = [{
        position: { lat: latlng.lat(), lng: latlng.lng() },
        label: 'New',
        map: null,
    }];

    /* Creates a new array for updating state. Is this the best way to do this */
    let markers = [...this.state.markers, ...newMarker] 
    this.setState({markers});

    console.log(this.state) // This shows the added marker
}

Something happens that results in the render() function of GoogleMap being called, but only the original markers are shown. The data is passed down to the GoogleMap component because I can see the output of console.log('render: ' + this.props.markers). But how do I get ALL the markers to load?

Please advise on what is the best way to for About to pass data to GoogleMap such that it can add in the new marker.