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

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

  // Note: QueuedTask is required to access the feature layer
  {
    var lyrDefLine = featureLayer.GetDefinition();

    // Define line chart CIM properties
    var lineChart = new CIMChart
    {
      Name = "lineChart",
      GeneralProperties = new CIMChartGeneralProperties
      {
        Title = $"Line chart for {dateField} summarized by {numericField}",
        UseAutomaticTitle = false
      },
      Series =
        [
            new CIMChartLineSeries {
              UniqueName = "lineChartSeries",
              Name = $"Sum({numericField})",
              // Specify date field and numeric field
              Fields = new string[] { dateField, numericField },
              // Specify aggregation type
              FieldAggregation = new string[] { string.Empty, "SUM" },
              // Specify custom time bin of 6 months
              TimeAggregationType = ChartTimeAggregationType.EqualIntervalsFromStartTime,
              TimeIntervalSize = 6.0,
              TimeIntervalUnits = esriTimeUnits.esriTimeUnitsMonths,
              // NOTE: When setting custom time binning, be sure to set CalculateAutomaticTimeInterval = false
              CalculateAutomaticTimeInterval = false,
              // Define custom line color
              ColorType = ChartColorType.CustomColor,
              LineSymbolProperties = new CIMChartLineSymbolProperties {
                  Style = ChartLineDashStyle.DashDot,
                  Color = new CIMRGBColor { R = 0, G = 150, B = 20 },
              },
              MarkerSymbolProperties = new CIMChartMarkerSymbolProperties
              {
                  Color = new CIMRGBColor { R = 0, G = 150, B = 20 }
              }
          },
      ]
    };

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