using System;

using System.Text.Json;                 

​

public class Program

{

    public static void Main()

    {

        var both = new Both{

            First = "A",

            Second = "B"

        };

        var bothJson = JsonSerializer.Serialize(both);

        Console.WriteLine($"bothJson: {bothJson}");

        var single = JsonSerializer.Deserialize<Single>(bothJson);

        var singleJson = JsonSerializer.Serialize(single);

        Console.WriteLine($"singleJson: {singleJson}");

    }

}

​

public class Single

{

    public string First {get; set;}

}

​

public class Both 

{

    public string First {get; set;}

    public string Second {get; set;}

}