// Setup dependency injection
var services = new ServiceCollection();
// use %TEMP%/TestFtpServer as root folder
services.Configure<DotNetFileSystemOptions>(opt => opt
    .RootPath = Path.Combine(Path.GetTempPath(), "TestFtpServer"));
// Add FTP server services
// DotNetFileSystemProvider = Use the .NET file system functionality
// AnonymousMembershipProvider = allow only anonymous logins
services.AddFtpServer(builder => builder
    .UseDotNetFileSystem() // Use the .NET file system functionality
    .EnableAnonymousAuthentication()); // allow anonymous logins
// Configure the FTP server
services.Configure<FtpServerOptions>(opt => opt.ServerAddress = "127.0.0.1");
// Build the service provider
using (var serviceProvider = services.BuildServiceProvider())
{
    // Initialize the FTP server
    var ftpServerHost = serviceProvider.GetRequiredService<IFtpServerHost>();
    // Start the FTP server
    ftpServerHost.StartAsync(CancellationToken.None).Wait();
    Console.WriteLine("Press ENTER/RETURN to close the test application.");
    Console.ReadLine();
    // Stop the FTP server
    ftpServerHost.StopAsync(CancellationToken.None).Wait();
}