JsonExtensionDataAttribute
When placed on a property or field of type JsonObject or
IDictionary<T, U>, any properties that do not have a
matching property or field are added during deserialization and written during serialization.
namespace System.Text.Json.Serialization
{
[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false)]
public sealed class JsonExtensionDataAttribute : JsonAttribute
{
}
}