aspnetcore3.0 Webapi JSON Serialization Deserialize<Dictionary<string, object> - asp.net

Question

i am use asp.net core 3.0 version for my project.
i create my webapi like this:
public IActionResult GetData()
{
var sql = "select * from aspnetusers";
var data = _base.GetDynamicBySql(sql) as List<IDictionary<string, object>>;
return Ok（data);
}
run the project and invoke the method,it give me a error info,it is like this:
Connection ID "18086456109425491997", Request ID "8000001f-0001-fb00-b63f-84710c7967bb": An unhandled exception was thrown by the application.
System.InvalidCastException: Unable to cast object of type '<GetEnumerator>d__9' to type 'System.Collections.IDictionaryEnumerator'.
at System.Text.Json.JsonSerializer.HandleDictionary(JsonClassInfo elementClassInfo, JsonSerializerOptions options, Utf8JsonWriter writer, WriteStack& state)
at System.Text.Json.JsonSerializer.Write(Utf8JsonWriter writer, Int32 originalWriterDepth, Int32 flushThreshold, JsonSerializerOptions options, WriteStack& state)
at System.Text.Json.JsonSerializer.WriteAsyncCore(Stream utf8Json, Object value, Type inputType, JsonSerializerOptions options, CancellationToken cancellationToken)
at Microsoft.AspNetCore.Mvc.Formatters.SystemTextJsonOutputFormatter.WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding)
at Microsoft.AspNetCore.Mvc.Formatters.SystemTextJsonOutputFormatter.WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResultFilterAsync>g__Awaited|29_0[TFilter,TFilterAsync](ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResultExecutedContextSealed context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext[TFilter,TFilterAsync](State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeResultFilters()
--- End of stack trace from previous location where exception was thrown ---
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|24_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeFilterPipelineAsync()
i know,asp.net core had removed the newtonsoft.json,and use System.Text.Json to change it.
i use the configure in my project.startup file like this
services.AddControllers().AddNewtonsoftJson(o =>
{
o.SerializerSettings.ContractResolver = new Newtonsoft.Json.Serialization.DefaultContractResolver();
})
But it still doesn't work.
the project can be work in asp.net core 2.0,I want to know how to confiure my project , i want set my project use Newtonsoft.Json for default .