<PackageReference Include="System.Configuration.ConfigurationManager" Version="10.0.1" />

System.Configuration.Internal.IInternalConfigConfigurationFactory

public interface IInternalConfigConfigurationFactory
Defines the interfaces used by the internal design time API to create a Configuration object.
Configuration Create(Type typeConfigHost, object[] hostInitConfigurationParams)

Creates and initializes a Configuration object.

string NormalizeLocationSubPath(string subPath, IConfigErrorInfo errorInfo)

Normalizes a location subpath of a path to a configuration file.