How to use new UseExceptionHandler and Error page in Blazor net8.0

I was pleased to read that Microsoft were introducing Error page support for Blazor in net8.0, see: https://learn.microsoft.com/en-us/aspnet/core/release-notes/aspnetcore-8.0?view=aspnetcore-8.0#error-page-support

So thought I would try it out. I created a new solution using the 'Blazor Web App' template, using the Server Interactive render mode and including the sample pages.

I then changed the Program.cs code to:

if (app.Environment.IsDevelopment()){    app.UseExceptionHandler("/Error", createScopeForErrors: true);    // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.    app.UseHsts();}

So that the error page should be used in development mode.

I then changed the Counter.razor IncrementCount method to:

private void IncrementCount(){    if (currentCount == 5)    {        throw new IndexOutOfRangeException("Counter can only go up to 5");    }    currentCount++;}

I ran the website in my local environment, clicking the counter Click me button. When it got to 5 the exception was thrown but rather than showing the error message it showed the usual blazor-error-ui message:

How do I get my Blazor application to show the error page instead?