WinAppDriver, Appium, C#, Connecting To An Already Running Window on Windows 10

Question

I'm trying to automate the use of an application with WinAppDriver and Appium on Windows 10 using C# .Net.

I'm trying to attach to an already running Window and I've been failing to find a way. I've tried many examples on the web, including from the github site for the WinAppDriver.

https://github.com/microsoft/WinAppDriver

I finally found a way to get a handle for the process, but when I try to connect it fails. It claims it's not a top level window.

The specific error is: "OpenQA.Selenium.WebDriverException: 'b2c is not a top level window handle'"

I've tried the "app" entry instead of "appTopLevelWindow", and it did not work.

Here is the code I'm running:

    private void grabWindowsProcesses2()
    {
        int number = 0;
        _txtBxOutput.Text = "";
        IntPtr myAppTopLevelWindowHandle = new IntPtr();
        foreach (Process clsProcess in Process.GetProcesses())
        {
            number++;

            _txtBxOutput.Text += number.ToString() + ") " + clsProcess.ProcessName + "\n";
            if (clsProcess.ProcessName.Contains("VisualBoyAdvance"))
            {
                myAppTopLevelWindowHandle = clsProcess.Handle;
                break;
            }
        }

        var appTopLevelWindowHandleHex = myAppTopLevelWindowHandle.ToString("x");

        AppiumOptions appCapabilities = new AppiumOptions();           
        appCapabilities.AddAdditionalCapability("platformName", "Windows");            
        appCapabilities.AddAdditionalCapability("deviceName", "WindowsPC");
        appCapabilities.AddAdditionalCapability("appTopLevelWindow", appTopLevelWindowHandleHex);

        /*
         * Error I get here is: OpenQA.Selenium.WebDriverException: 'b2c is not a top level window handle'
         */
        _visualBoyAdvance = new WindowsDriver<WindowsElement>(new Uri("http://127.0.0.1:4723"), appCapabilities);            
    }

Does anyone have any ideas about what I'm doing wrong? I'm fairly new to automating a desktop. I don't know, maybe there is a better way.