I think you referenced the .netstandard 2.x version of the ORMSupportClasses, but you should reference the normal one. The .netstandard 2.x version doesn't have any code in ConfigHelper, as netstandard 2.0 doesn't support config file reading.
If you used the nuget packages, make sure you have specified the right .net target in your csproj file. It might be you generated code for .netstandard20 which references the nuget packages by default but also specifies netstandard20 as targetdefinition in the csproj, so it'll reference the netstandard20 version of the ormsupport classes
