Localization not working in .NET6 Razor Pages project

I was trying to get localization to work in my 'real' project, but was not able to do so. So I created a new stock .NET6 Razor Pages project to test localization in a fresh environment. However I am not quite able to do that there as well. At this point I have read about 6 articles, watched 2 tutorials and read the official documentation which says that it is up to date with .NET6, but I'm not sure about that (partly because the examples use old syntax, i.e. not things that came with .NET6). Every single one of those resources more or less did/said the same things, which is what I have right now, but it just doesn't work.

This is my Program.cs file:

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddLocalization(options => options.ResourcesPath = "Resources");
//builder.Services.AddRazorPages(); builder.Services.AddMvc().AddDataAnnotationsLocalization();
builder.Services.AddRazorPages().AddDataAnnotationsLocalization();

var app = builder.Build();

if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Error");
    app.UseHsts();
}

app.UseHttpsRedirection();
app.UseStaticFiles();
app.UseRouting();

var supportedCultures = new[] { "en" };
var localizationOptions = new RequestLocalizationOptions().SetDefaultCulture(supportedCultures[0])
    .AddSupportedCultures(supportedCultures)
    .AddSupportedUICultures(supportedCultures);
app.UseRequestLocalization(localizationOptions);

app.UseAuthorization();
app.MapRazorPages();
app.Run();

I have tested the "things I'll mention bellow" with ...AddRazorPages().AddData... and (AddMvc().AddData... with ...AddRazorPages();) as well. That's why one of those lines is commented.

The way I am testing the localization is just with an OnGet call on the Index page, and restarting the (local) server after every change just to not miss some dumb thing. On the OnGet, I just log the value to the console. But I'm always getting the key. Here is the IndexModel class:

public class IndexModel : PageModel
{
    private readonly IStringLocalizer<IndexModel> _localizer;

    public IndexModel(IStringLocalizer<IndexModel> localizer)
    {
        _localizer = localizer;
    }

    public void OnGet()
    {
        Console.WriteLine(_localizer["Test"].Value);
    }
}

This is how my (relevant) folder structure looks like in the project's directory:

And finally the resx file:

Things I have tested are the .resx file names and the 2 possible locations. I am sure that both are correct, because when both files were active (neither had the .Dup (for duplicate) extension) at the end, I got an error from the compiler that multiple resources point to the same location or something like that. The names I have tested are the following:

IndexModel.en.resx
Index.en.resx
IndexModel.cshtml.cs.en.resx
Index.cshtml.cs.en.resx
IndexModel.cs.en.resx
Index.cs.en.resx