@이 상준 There are many differences for the In process (.NET Core 3.1) and Out of process (.NET 5.0) and the difference are covered in this document. You can see the difference in HTTP trigger that .NET Core 3.1 uses HttpRequest/ObjectResult whereas the .NET 5.0 now uses HttpRequestData/HttpResponseData
The HttpRequestData has Uri and Uri has property Query to get the value now in .NET 5.0
The stackoverflow covers the same and it is the right way of getting the query parameter value.