var solidStrokeSymbolLayer = new SolidStrokeSymbolLayer(solidStrokeSymbolLayer.Width, Color.Red)
{
    IsColorLocked = true,
    IsEnabled = true
};
var polygonSymbol = new MultilayerPolygonSymbol(new List<SymbolLayer>
{
    solidStrokeSymbolLayer
});
var vectorMarkerSymbolElements = new List<VectorMarkerSymbolElement>
{
    new VectorMarkerSymbolElement(geometry, polygonSymbol)
};
var vectorLayer = new VectorMarkerSymbolLayer(vectorMarkerSymbolElements)
{
    IsEnabled = true,
    IsColorLocked = true
};

var pointSymbol = new MultilayerPointSymbol(new List<SymbolLayer>
{
    vectorLayer
})
{
    Size = 30d
};