Curso Desatualizado:Alura Além do asp.net ser antigo, esta ocorrendo este problema System.NullReferenceException: 'Object reference not set to an instance of an object.'

Minha solução foi, essa na classe startup:

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
namespace CasaDoCodigoR
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllersWithViews();
            services.AddApplicationInsightsTelemetry();
            services.AddMvc();

            string connectionString = Configuration.GetConnectionString("Default");
            services.AddDbContext<ApplicationContext>(options => options.UseSqlServer(connectionString)
            );
            services.AddTransient <IDataService, DataService>();//Metodo addtransiente = instancia temporaria
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IServiceProvider serviceProvider)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }
            app.UseHttpsRedirection();
            app.UseStaticFiles();

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller=Pedido}/{action=Carrossel}/{id?}");
            });


            serviceProvider.GetService<IDataService>().InicializaDB();
        }


    }

}

Esta solução ainda continua com o erro CS6802, no asp.net 6.0

        serviceProvider.GetService<IDataService>().InicializaDB();


        porém no 3.1 funcionou.