Greetings from Syncfusion,
We have validated your requirement and we would like to let you know that in UWP there is not GetStream method instead we can use the ImageStream to get the convert the chart as image. Also, there is a framework level limitation in UWP in getting the stream on the fly. So, you need to add the chart in the view in order to convert that as an image stream. To learn more on this limitation, please refer the below link.
So, to get the chart as image in UWP you can use SaveAsImage method as like in below code snippet.
Code Snippet C#
private void Button_Clicked(object sender, EventArgs e)
We have prepared a sample to convert the chart into image and the sample can be downloaded from the below link.
Let us know if you need any other assistance from us.