Hi Durgesh,
Thank you for posting here.
As far as I know, the & symbol should belong to LowerCodeCharts.BasicLatin, but I don't know why it failed.

Finally I had to give up Microsoft.Security.Application and use System.Web.HttpUtilit instead.
This class is easy to use and seems to be more comprehensive.
This is my code:
String str = "Βρε&&";
//System.Web.HttpUtilit
String data = System.Web.HttpUtility.HtmlEncode(str);
StringWriter myWriter = new StringWriter();
// Decode the encoded string.
HttpUtility.HtmlDecode(data, myWriter);
string myDecodedString = myWriter.ToString();
Console.WriteLine($"Decoded string of the above encoded string is: {myDecodedString}");
Result:

Hope this could be helpful.
Best Regards,
Timon
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