C#

using Microsoft.Extensions.DependencyInjection;

static class Program
{
    public static IServiceProvider ServiceProvider { get; private set; }
    
    private static void ConfigureServices(IServiceCollection services)
    {
        ...
    }
    
    static void Main()
    {
        var services = new ServiceCollection();
        ConfigureServices(services);
        ServiceProvider = services.BuildServiceProvider();
        ...
    }
}

private static void ConfigureServices(IServiceCollection services)
{
    services.AddScoped<MainForm>();
    services.AddScoped<MenuForm>();
    services.AddScoped<AmazonForm>();
    services.AddScoped<AmazonDownloadForm>();
    services.AddScoped<AmazonOrderDialogForm>();
    services.AddScoped<AmazonViewOrdersForm>();
    services.AddScoped<DownloadFileProcessorDialog>();
    services.AddScoped<EBayForm>();
    services.AddScoped<EBayDownloadForm>();            

<pre>
services.AddTransient<IOrdersRepository, OrdersRepository>();
services.AddSingleton<IGmailSender, GmailSender>();

using (ServiceProvider serviceProvider = services.BuildServiceProvider())
{
    var mainForm = serviceProvider.GetRequiredService<MainForm>();
    mainForm.Shown += Main_Shown;
    mainForm.FormClosed += Main_FormClosed;

    // Run the Main Form
    Application.Run(mainForm);
} 

var menuForm = new MenuForm(_ordersRepository)
{
   MdiParent = this,
   Dock = DockStyle.Fill
};
menuForm.Show();

private void Btn_Amazon_Click(object sender, EventArgs e)
{
    // close all the open forms
    for (var i = Application.OpenForms.Count - 1; i >= 1; i += -1)
    {
        var form = Application.OpenForms[i];
        if (form.Name != "MainForm")
            form.Close();
    }

    var amazonForm = new AmazonForm(_ordersRepository)
    {
        MdiParent = MainForm.ActiveForm,
        Dock = DockStyle.Fill
    };
    amazonForm.Show();
    Application.DoEvents();
}

var dbCredentialsFormDI = serviceProvider.GetRequiredService<DbCredentialsForm>();
dbCredentialsFormDI.firstTime = false;
dbCredentialsFormDI.Dock = DockStyle.None;
dbCredentialsFormDI.StartPosition = FormStartPosition.CenterScreen;

var result = dbCredentialsFormDI.ShowDialog();
if (result == DialogResult.OK)
{
    Application.DoEvents();
}

public partial class DbCredentialsForm : Form
{
    private readonly bool _firstTime;

    public DbCredentialsForm(bool firstTime)
    {
        InitializeComponent();
        _firstTime = firstTime;
        OK_Button.Enabled = false;
    }

public partial class DbCredentialsForm : Form
{
    public bool firstTime { get; set; }

    public DbCredentialsForm()
    {
        InitializeComponent();           
       OK_Button.Enabled = false;
    }

public class Foo
{
    public IBar Bar { get; }
    public IBaz Baz { get; }
    public Foo(IBar bar = default, IBaz baz = default) (Bar, Baz) = (bar, baz);
}

...

IServiceCollection services = new ServiceCollection();
services.AddTransient<IBaz, Baz>();
services.AddTransient<Foo>();

IServiceProvider provider = services.BuildServiceProvider();
Foo foo = provider.GetRequiredService<Foo>();

Debug.Assert(foo != null);
Debug.Assert(foo.Baz != null);
Debug.Assert(foo.Bar == null);

using static System.Console;
...
WriteLine("Foo"); // Calls System.Console.WriteLine("Foo");

Richard Deeming wrote:

of that type available with prefixing them