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/v2/CIMCharts.md

// Define fields names used in chart parameters.
const string dateField = "last_review";
const string numericField = "price";

var lyrsLine = MapView.Active.Map.GetLayersAsFlattenedList().OfType<FeatureLayer>();
var lyrLine = lyrsLine.First();
var lyrDefLine = lyrLine.GetDefinition();

// Define line chart CIM properties
var lineChart = new CIMChart
{
    Name = "lineChart",
    GeneralProperties = new CIMChartGeneralProperties
    {
        Title = $"Line chart for {dateField} summarized by {numericField}",
    },
    Series = new CIMChartSeries[]
    {
    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 },
        }
    },
    }
};

// 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 defintion 
lyrDefLine.Charts = allChartsLine.ToArray();
lyrLine.SetDefinition(lyrDefLine);