You were missing the System.Data.DataSetExtensions NuGet package for net48, you can install it as a dependency just for net48 by adding a condition to the package reference (see attached)
The designer only works when you have NET48 included as a TargetFramework in your application, we have plans for a .NET Core designer but it’s still in the works.
Yes, ultimately it’s not a Wisej.NET issue, it’s more of a missing package in your project!
Attached is a modified version of your sample, it works fine now!
