The RadUpload control has been discontinued in June 2013 (Q2’13), as stated in the help article you pointed. Thus, there is no development or support for it and support for new browsers is not included in it.
The article also points resources how you could migrate your RadUpload to its successor - the RadAsyncUpload
control, which supports both MS Edge and Google Chrome browsers, in comparison to the RadUpload. I would suggest you to evaluate the RadAsyncUpload
and use it instead, if you are required to run your project on MS Edge.
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