public class CIMChartBarSeries : CIMChartSeries, System.ComponentModel.INotifyPropertyChanged, System.Xml.Serialization.IXmlSerializable  

{
  // Note: QueuedTask is required to access the feature layer
  {
    var layerDefinition = featureLayer.GetDefinition();
    string fieldXAxis = "textField";
    string fieldYAxis = "NumericField";

    var myBarChart = new CIMChart
    {
      Name = "Bar chart",
      GeneralProperties = new CIMChartGeneralProperties
      {
        Title = $"{fieldXAxis} vs. {fieldYAxis}",
        UseAutomaticTitle = false
      },
      Series =
      [
          new CIMChartBarSeries
      {
        Name = "Bar chart",
        UniqueName = "Bar chart",
        Fields = new string[] { fieldXAxis, fieldYAxis },
        //Create green fill symbols
        FillSymbolProperties = new CIMChartFillSymbolProperties
          {
            Color = CIMColor.CreateRGBColor(38, 115, 0, 70)
          }
      }
      ]
    };
    // Add new chart to layer's existing list of charts (if any exist)
    var newBarCharts = new CIMChart[] { myBarChart };
    var allChartsBar = (layerDefinition.Charts == null) ? newBarCharts : layerDefinition.Charts.Concat(newBarCharts);
    // Add CIM chart to layer definition 
    layerDefinition.Charts = allChartsBar.ToArray();
    featureLayer.SetDefinition(layerDefinition);
  }

}

{
  // For more information on the chart CIM specification:
  // https://github.com/Esri/cim-spec/blob/main/docs/v3/CIMCharts.md

  var lyrDefBar = featureLayer.GetDefinition();

  // Get unique values for `splitByField`
  var values = new List<string>();
  using (RowCursor cursor = featureLayer.Search())
  {
    while (cursor.MoveNext())
    {
      var value = Convert.ToString(cursor.Current[splitByField]);
      values.Add(value);
    }
  }
  ;
  var uniqueValues = values.Distinct().ToList();

  // Define bar chart CIM properties
  var barChart = new CIMChart
  {
    Name = "barChart",
    GeneralProperties = new CIMChartGeneralProperties
    {
      Title = $"{categoryField} grouped by {splitByField}",
      UseAutomaticTitle = false
    },
  };

  // Create list to store the info for each chart series
  var allSeries = new List<CIMChartSeries>();

  // Create a series for each unique category
  foreach (var value in uniqueValues)
  {
    var series = new CIMChartBarSeries
    {
      UniqueName = value,
      Name = value,
      // Specify the category field
      Fields = new string[] { categoryField, string.Empty },
      // Specify the WhereClause to filter a series by unique value
      WhereClause = $"{splitByField} = '{value}'",
      GroupFields = new[] { categoryField },
      // Specify aggregation type
      FieldAggregation = new string[] { string.Empty, "COUNT" }
    };

    allSeries.Add(series);
  }

  barChart.Series = allSeries.ToArray();

  // Add new chart to layer's existing list of charts (if any exist)
  var newChartsBar = new CIMChart[] { barChart };
  var allBarCharts = (lyrDefBar == null) ? newChartsBar : lyrDefBar.Charts.Concat(newChartsBar);
  // Add CIM chart to layer definition 
  lyrDefBar.Charts = allBarCharts.ToArray();
  featureLayer.SetDefinition(lyrDefBar);
}