using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        Parent parent = new() { Id = 1, Name = "Parent", AdditionalProperties = new Dictionary<string, object>() { { "Property", "SomeProperty" } } };

​

        var newtonSoftJson = Newtonsoft.Json.JsonConvert.SerializeObject(parent);

        Console.WriteLine(newtonSoftJson);

​

        var microsoftJson = System.Text.Json.JsonSerializer.Serialize(parent);

        Console.WriteLine(microsoftJson);

    }

}

​

public class Parent

{

    public int Id { get; set; }

    public string Name { get; set; }

​

    [System.Text.Json.Serialization.JsonExtensionData]

    [Newtonsoft.Json.JsonExtensionData]

    public Dictionary<string, object> AdditionalProperties { get; set; }

}

​