EdmModel with generic class

I have a generic class that I want to expose in the EdmModel. The issue is the result obtained from OData, I am not showing all data.

This is the schema to be returned from the endpoint.

[
  {
    "item": {
      "id": "string",
      "resourceType": "string",
    },
    "etag": "string"
  }
]

And this is the result when calling the endpoint. For any reason item is not showed.

{
  "@odata.context": "https://localhost:44397/api/v1/Admin/$metadata#appConfig",
  "value": [
    {
      "Etag": "Ayj8F2FzRxbqHYPrYj2Mti0pSW5lxGTZ6womMFuGWUg="
    },
    {
      "Etag": "8KcnnNKf5g7VHP7+NHqUjlhv57Ym7F0VQpSykD9a04I="
    },
    {
      "Etag": "LGR1OCClN6llYGTw+JZIwDOJ2zG+qXU6kLPhWRS4voU="
    }
  ]
}

The action in the controller is defined as follow

[HttpGet("appConfig")]
[EnableQuery()]
public Task<IEnumerable<EtagItem<AppConfig>>> GetAppConfigAsync()
{
    return GraphService.GetAppConfigAsync();
}

EdmModel is created like this. I tried to define an EntityType but I obtained the same result.

public static IEdmModel GetAdminEdmModel(this IServiceProvider serviceProvider)
{
    var builder = new ODataConventionModelBuilder(serviceProvider);
    builder.EntitySet<EtagItem<AppConfig>>("appConfig");
    //builder.EntityType<AppConfig>();
    //builder.EntityType<UserAppConfig>();
    //builder.EntityType<GroupAppConfig>();

    return builder.GetEdmModel();
}

And these are the classes, where IModelItem only exposes Id property and UserAppConfig and GroupAppConfig inherited from base class.

public sealed class EtagItem<TDocument> where TDocument : IModelItem
{
    [JsonProperty(Required = Required.Always)]
    public TDocument Item { get; set; }

    [Key]
    [JsonProperty(Required = Required.Always)]
    public string Etag { get; set; }
}

public abstract class AppConfig : IModelItem
{
    public string Id { get; set; }

    public string ResourceType { get; set; }
}