public class CIMChartScatterSeries : 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 xField = "minimum_nights";
const string yField = "price";

var lyrsScatter = MapView.Active.Map.GetLayersAsFlattenedList().OfType<FeatureLayer>();
var lyrScatter = lyrsScatter.First();
var lyrDefScatter = lyrScatter.GetDefinition();

// Define scatter plot CIM properties
var scatterPlot = new CIMChart
{
    Name = "scatterPlot",
    GeneralProperties = new CIMChartGeneralProperties
    {
        Title = $"{xField} vs. {yField}",
    },
    Series = new CIMChartSeries[]
    {
    new CIMChartScatterSeries {
        UniqueName = "scatterPlotSeries",
        Name = "scatterPlotSeries",
        // Specify the X and Y field names
        Fields = new string[] { xField , yField },
        // Turn on trend line
        ShowTrendLine = true
    }
    }
};

// Add new chart to layer's existing list of charts (if any exist)
var newChartsScatter = new CIMChart[] { scatterPlot };
var allChartsScatter = (lyrDefScatter == null) ? newChartsScatter : lyrDefScatter.Charts.Concat(newChartsScatter);
// Add CIM chart to layer defintion 
lyrDefScatter.Charts = allChartsScatter.ToArray();
lyrScatter.SetDefinition(lyrDefScatter);