C# newtonsoft.json append json object from json object format

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JSON.NET

I'm new in Json, already searching many info but no luck, based on:
json add new object to existing json file C# - Stack Overflow[^] (have tried it, and it's works)
But that needs an array json format (begin with [ , ends with ]), mine is object json format (begin with { , ends with }).
So, how to do that in Newtonsoft.Json without change the json into Json array format?



my Json (object):

{
  "Group": "Group1",
  "ID": 1,
  "Name": "Author1",
  "Description": "Desc1"
}

Using this to create it:

class Author
{
  public string Group { get; set; }
  public int ID { get; set; }
  public string Name { get; set; }
  public string Description { get; set; }
}

private Author NewAuthor()
{
  Author author = new Author()
  {
  Group = "Group1",
  ID = 1,
  Name = "Author1",
  Description = "Desc1"
  };
  return author;
}

private void Btn_Create_Click(object sender, EventArgs e)
{
  string jsonData = JsonConvert.SerializeObject(NewAuthor(), Formatting.Indented);
  File.WriteAllText(Filepath, jsonData);
}

Desired output:

{
  "Group": "Group1",
  "ID": 1,
  "Name": "Author1",
  "Description": "Desc1"
},
{
  "Group": "Group2",
  "ID": 2,
  "Name": "Author2",
  "Description": "Desc2"
}

What I have tried:

Based on json add new object to existing json file C# - Stack Overflow[^]
below code works, but when the json begin with [ not {

Author author = NewAuthor();
var lst = JsonConvert.DeserializeObject<List<Author>>(json) ?? new List<Author>();
lst.Add(author);

// Write to file
string updatedJson = JsonConvert.SerializeObject(lst, Formatting.Indented);
File.WriteAllText(filepath, updatedJson);