Google.Protobuf.dll is right next to my .dll but it is not being found or loaded

I have a Framework 4.8 C# app that uses ClearScript to allow JavaScript to be used as an extension language. I am able to write plugins as DLLs and attach them at runtime, viz

JSE.Script.attach = (Func<string, bool>)Attach;
...
        private static bool Attach(string dllPath, string name = "")
        {
            var status = false;
            var htc = new HostTypeCollection();
            try
            {
                var assem = Assembly.Load(AssemblyName.GetAssemblyName(dllPath));
                htc.AddAssembly(assem);
                if (name.Length == 0)
                {
                    name = assem.FullName.Split(',')[0];
                }

                JSE.AddHostObject(name, htc); //FIXME checkout the hosttypes
                Console.Error.WriteLine($"Attached {dllPath} as {name}");
                status = true;
            }
            catch (ReflectionTypeLoadException rtle)
            {
                foreach (var item in rtle.LoaderExceptions)
                {
                    Console.Error.WriteLine(item.Message);
                    T.Fail(item.Message);
                }

            }
            catch (FileNotFoundException fnfe)
            {
                Console.Error.WriteLine(fnfe.Message);
                T.Fail(fnfe.Message);

            }
            catch (Exception e)
            {
                Console.Error.WriteLine(e.Message);
                T.Fail(e.Message);

            }
            return status;
        }

This permits my scripts to have lines like

attach(".\\Plugin_GoogleAds_Metrics.dll");
H = Plugin_GoogleAds_Metrics.GoogleAds_Metrics.Historical;
H.EnableTrace("GAM");
...

I've made a public repo of the plugin for those interested.

What's not working in this situation is that when I try to execute the plugin's GetAccountInformation method, and execution reaches the GoogleAdsServiceClient googleAdsService = client.GetService(Services.V11.GoogleAdsService); line, an error is thrown complaining about Google.Protobuf, viz

Exception has been thrown by the target of an invocation.
    at JScript global code (Script [23] [temp]:5:0) -> acc = H.GetAccountInformation(auths.Item1, 7273576109, true)
   at Microsoft.ClearScript.ScriptEngine.ThrowScriptError(IScriptEngineException scriptError)
   at Microsoft.ClearScript.Windows.WindowsScriptEngine.ThrowScriptError(Exception exception)
   at Microsoft.ClearScript.Windows.WindowsScriptEngine.<>c__DisplayClass57_0`1.<ScriptInvoke>b__0()
   at Microsoft.ClearScript.ScriptEngine.ScriptInvokeInternal[T](Func`1 func)
   at Microsoft.ClearScript.ScriptEngine.ScriptInvoke[T](Func`1 func)
   at Microsoft.ClearScript.Windows.WindowsScriptEngine.ScriptInvoke[T](Func`1 func)
   at Microsoft.ClearScript.Windows.WindowsScriptEngine.Execute(UniqueDocumentInfo documentInfo, String code, Boolean evaluate)
   at Microsoft.ClearScript.Windows.JScriptEngine.Execute(UniqueDocumentInfo documentInfo, String code, Boolean evaluate)
   at Microsoft.ClearScript.ScriptEngine.Evaluate(UniqueDocumentInfo documentInfo, String code, Boolean marshalResult)
   at Microsoft.ClearScript.ScriptEngine.Evaluate(DocumentInfo documentInfo, String code)
   at Microsoft.ClearScript.ScriptEngine.Evaluate(String documentName, Boolean discard, String code)
   at Microsoft.ClearScript.ScriptEngine.Evaluate(String documentName, String code)
   at Microsoft.ClearScript.ScriptEngine.Evaluate(String code)
   at RulesetRunner.Program.Run(JScriptEngine& jSE, String scriptText, Config cfg, Dictionary`2 settings) in C:\Users\bugma\Source\Repos\Present\BORR\RulesetRunner\RunManagementPartials.cs:line 72
Exception has been thrown by the target of an invocation.
Exception has been thrown by the target of an invocation.
Could not load file or assembly 'Google.Protobuf, Version=3.15.8.0, Culture=neutral, PublicKeyToken=a7d26565bac4d604' or one of its dependencies. The system cannot find the file specified.

So

1. I am using the latest Google.Ads.GoogleAds library
2. AutoGenerateBindingRedirects has been set to true in the csproj file
3. Add-BindingRedirect has been executed in the context of the Plugin's project
4. The Plugin_GoogleAds_Metrics.dll is in the same folder as the Google.Protobuf.dll

Where to from here?