Starting in .NET 8, the affected methods throw a NotSupportedException at run time across all project types except Windows Forms and WPF. The APIs continue to remain obsolete (as error) across all project types, including Windows Forms and WPF.

Functions like: CreateRestorePoint SaveAsBinary LoadFromBinary uses BinaryFormatter and in .net8-windows i get SerializationException from System.CoreLib

Inner Exception :
Source :System.Private.CoreLib
Message :Serializing delegates is not supported on this platform.
Type :System.Runtime.Serialization.SerializationException
Stack trace : at System.MulticastDelegate.GetObjectData(SerializationInfo info, StreamingContext context)
at System.Runtime.Serialization.Formatters.Binary.WriteObjectInfo.InitSerialize(Object obj, ISurrogateSelector surrogateSelector, StreamingContext context, SerObjectInfoInit serObjectInfoInit, IFormatterConverter converter, ObjectWriter objectWriter, SerializationBinder binder)
at System.Runtime.Serialization.Formatters.Binary.ObjectWriter.Write(WriteObjectInfo objectInfo, NameInfo memberNameInfo, NameInfo typeNameInfo)
at System.Runtime.Serialization.Formatters.Binary.ObjectWriter.Serialize(Object graph, BinaryFormatterWriter serWriter)
at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Serialize(Stream serializationStream, Object graph)
at Infragistics.Win.UltraWinToolbars.UltraToolbarsManager.SaveHelper(Stream stream, IFormatter formatter)

Breaking change: BinaryFormatter disabled across most project types - .NET | Microsoft Learn

learn.microsoft.com/.../system.runtime.serialization.serializationexception