Why doesn't vscode return error when calling an async method from a non-async wrapper method?

Question

I have the following code that works fine as is - aka no errors and it builds / runs:

if (featureManager.IsEnabledAsync("FeatureToggleABC").Result)
{
    backgroundTask.Run<NewToggleUserTask>(u => u.AddUserIntoGroup(userName, groupName, connParam));
    return "Running task with new toggle";
}

Per Microsoft, it's best NOT to use strings for toggle names incase we finger fumble. It will just assume that the name is still a legit toggle, and set the value to false.

So I've created an enum like this:

namespace Widgets.Enums
{
    public enum WidgetFeatureFlags
    {
        FeatureToggleABC
    }
}

And i've tried to change the if statement to look like this:

if (featureManager.IsEnabledAsync(nameof(WidgetFeatureFlags.FeatureToggleABC)).Result)
{
    backgroundTask.Run<NewToggleUserTask>(u => u.AddUserIntoGroup(userName, groupName, connParam));
    return "Running task with new toggle";
}

But I'm getting an error that says:

Cannot implicitly convert type 'System.Threading.Tasks.Task' to 'bool'

This works:

var featureName = nameof(WidgetFeatureFlags.FeatureToggleABC);
if (featureManager.IsEnabledAsync(featureName).Result)
{

I'm sure it's something simple I've missed but I haven't been able to resolve it. I've tried casting the results but so far no dice.

EDIT 1

Method signatures:

    Task<bool> IsEnabledAsync(string feature);

And the method that calls IsEnabledAsync:

 public string GetUserMember(string userName, string groupName, string tName)

Edit 2

The featureManager is created using this IFeatureManager class:

namespace Microsoft.FeatureManagement
{
    //
    // Summary:
    //     Used to evaluate whether a feature is enabled or disabled.
    public interface IFeatureManager
    {

     IAsyncEnumerable<string> GetFeatureNamesAsync();
     Task<bool> IsEnabledAsync(string feature); 
     Task<bool> IsEnabledAsync<TContext>(string feature, TContext context);
    }
}