.Net core OData with EDM troubles

Thanks for the article!
I seem to be having mixed results trying to get my code working.
I'm running .net core 2.1 and Microsoft.AspNetCore.OData Version=7.1.0.
My startup extensions:
    // invoked from startup, ConfigureServices()
public static IServiceCollection AddODataSupport(this IServiceCollection services)
{
    services.AddOData();
    //Workaround: https://github.com/OData/WebApi/issues/1177
    services.AddMvcCore(options =>
    {
        foreach (var outputFormatter in options.OutputFormatters.OfType<ODataOutputFormatter>()
            .Where(_ => _.SupportedMediaTypes.Count == 0))
        {
            outputFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("application/prs.odatatestxx-odata"));
        }
        foreach (var inputFormatter in options.InputFormatters.OfType<ODataInputFormatter>()
            .Where(_ => _.SupportedMediaTypes.Count == 0))
        {
            inputFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("application/prs.odatatestxx-odata"));
        }
    });
    return services;
}

 // invoked from startup, app.UseMVC()
public static void ConfigureODataRouting(this IRouteBuilder routeBuilder)
{
    routeBuilder.EnableDependencyInjection();
    routeBuilder.Select().Filter().OrderBy().Expand().Count().MaxTop(100);routeBuilder.MapODataServiceRoute("odata", "odata", GetEdmModel());
}

private static IEdmModel GetEdmModel()
{
    var obuilder = new ODataConventionModelBuilder();
    obuilder.EntitySet<TransactionEntity>("Transactions");
    return obuilder.GetEdmModel();
}
Here's my controller:

public class ODataController : ControllerBase
{
    private readonly ITmDataContext dataContext;
    public ODataController(ITmDataContext dataContext)
    {
        this.dataContext = dataContext;
    }

    [Route("odata/transactions")]
    [HttpGet]
    [EnableQuery]
    public ActionResult<IEnumerable<object>> GetTransactions()
    {
        return dataContext.Transactions;
    }
 }
I can hit the $metadata endpoint and get my edm xml.

<?xml version="1.0" encoding="utf-8"?><edmx:Edmx Version="4.0" xmlns:edmx="http://docs.oasis-open.org/odata/ns/edmx"><edmx:DataServices><Schema Namespace="TMS.DataManagement.Service.Data.Entities" xmlns="http://docs.oasis-open.org/odata/ns/edm"><EntityType Name="TransactionEntity"><Key><PropertyRef Name="Id" /></Key><Property Name="Id" Type="Edm.Int32" Nullable="false" /> ...

and I can hit the odata/Transactions endpoint.
    HTTP GET https://localhost:5001/odata/Transactions returns data like
    [
        {
          "id": 2860,
          "school_id": 3,
          "type_code": 1,
          "post_status_code": 0,
          "post_date": "2019-07-01T00:00:00",
          "deleted": true,
          "description": "fee name",
          "comments": "",
          "insert_date": "2019-07-01T11:35:48.2343931",
          "modified_date": "2019-07-02T17:24:35.5232986",
          "last_modify_user_id": 100169
        }
     ,... etc
    ]
BUT:
1) my results never have the edm metadata (payload is missing the "@odata.context" node)
2) some operations like $expand and $filter work, but others like $count=true don't include the count node.
3) If I try to consume my odata feed in a client application (like excel), I get an error
    'StartArray' node was found when reading from the JSON reader. A 'StartObject' node was expected.

If I remove the [Route] attribute on my endpoint as you suggested, I can't hit the odata/transactions endpoint. I get a 404.
All of the above makes me think I haven't implemented the OData routing correctly, but I'm not sure where I've messed up.
Any thoughts?