Startup.cs를 .NET 6 프로젝트에 다시 추가

public class Startup
{
    readonly IConfiguration configuration;

    public Startup(IConfiguration configuration)
    {
        this.configuration = configuration ?? throw new ArgumentNullException(nameof(configuration));
    }

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddControllers();
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        app.UseRouting();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapDefaultControllerRoute();
        });
    }
}

//add necessary usings

var builder = WebApplication.CreateBuilder(args);

//create new instance of Startup
var startup = new Startup(builder.Configuration);

//configure all services
startup.ConfigureServices(builder.Services);

var app = builder.Build();

//configure the pipeline
startup.Configure(app, builder.Environment);

//run
app.Run();