Default page middleware could not return the default page '/index.html' because it was not found -

Question

I am trying to run a [.NET Core + Angular] project, but encountering a bunch of errors. The .NET Core version of the project is 3.1.

The very first error I got was:

The NPM script 'start' exited without indicating that the Angular CLI was listening for requests.

So, I consulted THIS resource -> https://www.c-sharpcorner.com/blogs/the-npm-script-start-exited-without-indicating-that-the-createreact and accordingly proceeded to comment out the snippet under IsDevelopment().

Which again, led to this current error I have posted in the question title.

I consulted few resources, and according to one of them added the following piece of code in Startup.cs:

spa.Options.SourcePath = "ClientApp/dist";

That doesn't resolve it. Mind you, I am not deploying to Azure or IIS, simply launching the project from Visual Studio 2022.

I checked angular.json of ClientApp and found that "outputPath": "dist" is set there in the 'build' section.

If you follow THIS resource-> https://learn.microsoft.com/en-us/answers/questions/1624504/invalidoperationexception-the-spa-default-page-mid it tells you to configure Startup.cs further as:

app.UseStaticFiles(new StaticFileOptions
            {
                FileProvider = new PhysicalFileProvider(
                Path.Combine(app.Environment.ContentRootPath, "ClientApp", "dist")),
                RequestPath = ""
            });

But applying that code causes this error

'IApplicationBuilder' does not contain a definition for 'Environment' and no accessible extension method 'Environment' accepting a first argument of type 'IApplicationBuilder' could be found (are you missing a using directive or an assembly reference?)

In the launchSettings.json file I checked that the env. variable is set to "Development":

"environmentVariables": {
      "ASPNETCORE_ENVIRONMENT": "Development"
}

As last ditch attempt, I experimented with adding the following 2 lines in the .csproj project file:

<Content Include="ClientApp\dist\**">
<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>

This corrupts the whole project, and it does not load.

So what's all this ruckus about? How do I get this SPA .NET Core + Angular project launching without these glitches? Let me know, if you need more details about project configuration, settings etc to understand the cause of this misbehavior. Will share.

Thanks,