<PackageReference Include="System.Configuration.ConfigurationManager" Version="8.0.0-preview.7.23375.6" />

SettingsSerializeAs

public enum SettingsSerializeAs
Determines the serialization scheme used to store application settings.
namespace System.Configuration { public enum SettingsSerializeAs { String, Xml, [System.Obsolete("BinaryFormatter serialization is obsolete and should not be used. See https://aka.ms/binaryformatter for more information.. Consider using Xml instead.")] Binary, ProviderSpecific } }