<PackageReference Include="System.Configuration.ConfigurationManager" Version="9.0.0-preview.5.24306.7" />

SettingsProviderAttribute

public sealed class SettingsProviderAttribute : Attribute
Specifies the settings provider used to provide storage for the current application settings class or property. This class cannot be inherited.
namespace System.Configuration { [AttributeUsage(AttributeTargets.Class | AttributeTargets.Property)] public sealed class SettingsProviderAttribute : Attribute { private readonly string _providerTypeName; public string ProviderTypeName => _providerTypeName; public SettingsProviderAttribute(string providerTypeName) { _providerTypeName = providerTypeName; } public SettingsProviderAttribute(Type providerType) { if (providerType != (Type)null) _providerTypeName = providerType.AssemblyQualifiedName; } } }