Simple Pie Chart not working in custom module. Do you see any errors in my code?

I am running Drupal 9 in Lando. I have enabled the Charts and Highcharts modules and installed the Highcharts JS library with composer. I wrote a simple module to display a Pie Chart but the chart won't display. My code is below. Do you see any glaring errors or ways I can debug this? I ported this from an example that runs fine in D7 in DevDesktop.
The info yaml file.

name: My Test Chart
description: This is an example use of the Charts module.
package: Custom
type: module
core_version_requirement: ^9
dependencies:
  - chart

The router yaml file.

example_chart:
  path: 'mychart-example'
  defaults:
    _title: 'My Example Chart'
    _controller: '\Drupal\mychart\Controller\MyChartController::example_page'
  requirements:
    _permission: 'access content'

The library yaml file.

highcharts:
  js:
    libraries/highcharts/highcharts.js: {  }
  dependencies:
    - core/jquery

The Controller.

namespace Drupal\mychart\Controller;

use Drupal\Core\Controller\ControllerBase;

class MyChartController extends ControllerBase {
  /**
   * @return array
   */
  function example_page() {
    $chart = array(
      '#attached' => array(
        'library' => array('mychart/highcharts'),
      ),
      '#type' => 'chart',
      '#chart_type' => 'pie',
      '#chart_library' => 'highcharts',
      '#title' => t('Simple Pie Chart'),
    );
    $chart['pie_data'] = array(
      '#type' => 'chart_data',
      '#title' => t('Gender'),
      '#data' => array(array('Male', 10), array('Female', 20)),
    );
    return  $chart;
  }
}

The solution was upgrading the Charts module to version 5.0.x. Now my simple pie chart works!