Azure B2C - PublicClientApplicatcion.AcquireTokenByUsernamePasswordAsync fails

I have trouble to sign in to my Azure B2C Active Directory with username and password from .net core console app. I am using the MSAL Library 2.6 from nuget. I found this example on GitHub https://github.com/Azure-Samples/active-directory-dotnetcore-console-up-v2

I reduced the code to a minimum it looks like this:

public static async Task TestLogin()
{
    try
    {
        var scopes = new[] { "community.member" };
        var username = "{user@domain.com}";
        var password = new SecureString();

        foreach (var c in "{Password}")
        {
            password.AppendChar(c);
        }

        var app = new PublicClientApplication("{B2C Application ID}", "https://{Application Name}.b2clogin.com/tfp/xxxxxxx-xxxx-xxxxxxxxxxxx/B2C_1_NativeSigneIn");

        var result = await app.AcquireTokenByUsernamePasswordAsync(scopes, username, password);
        Console.WriteLine($"Token: {result.AccessToken}");
    }
    catch (MsalServiceException ex)
    {
        Console.WriteLine($"{ex.Message} - {ex.ErrorCode}");
    }
}

I am always getting the following MSAL exception: Message: User realm discovery failed ErrorCode: user_realm_discovery_failed