Azure B2C authentication using ASP.NET Core 1.1.7 and Microsoft Identity Provider

I have a web application using .NET Framework 4.7.2 + ASP.NET Core 1.1.7 and I want to implement on it user authentication using Microsoft Azure B2C.

The idea is to add from the Azure B2C portal what users can log in by exclusively adding their already-existing Microsoft Account, i.e. they should log in using the following form:

These users are meant to be internal users of the organization only and they must not sign-up themselves via any kind of sign-up form.

I have already created a policy for Signing In and configured Microsoft Account on it as an Identity Provider:

However, I constantly get the following error message when launching the app, where I expect me to be redirected to the Microsoft Account Login Page:

Can I achieve this goal (make users login via their Microsoft Account) given the current scenario (web app with .NET Framework 4.7.2 + ASP.NET Core 1.1.7)?

I'd like to try to avoid any framework update if possible as it is very likely to introduce important breaking changes in the app.

Possible hint: according to this Microsoft documentation, the most suitable configuration for this use case should be the following:

which I can only set for an app being registered with the following second option (legacy), not with the first one: