Convert string with escape characters in json object in .net core 3.1

con.Open();
MySqlParameter _ReturnValue = new MySqlParameter("_ReturnValue", MySqlDbType.Int32);
_ReturnValue.Direction = System.Data.ParameterDirection.Output;
cmd.Parameters.Add(_ReturnValue);
using (var parser = new ChoJSONWriter(sb))
parser.Write(cmd.ExecuteReader());

Now what sb.ToString() is returning is: "[\n {\n \"code\": \"SC0009\"\n }\n]"

and just wanted to convert this to an object, for the same in .net core 2.1, below code was working fine:

private JToken ParseStrtoJson(string strv)
    {
        JToken token = JToken.Parse(@strv);
        return token;
    }

After upgrade to .net Core 3.1, it is returning what I receive in webapi result is this:

"code": [
        [
            [
                []
            ]
        ]
    ]

Which is quite not clear with and how to handle it.

In asp.net core 3.1, for the operation of json class, Microsoft.AspNetCore.Mvc.NewtonsoftJson needs to be installed.

And add the following to the ConfigureServices method of Startup.cs：

   public void ConfigureServices(IServiceCollection services)
    {
       services.AddControllers().AddNewtonsoftJson();
    }

You can refer to this.