Using middleware in ASP.NET Core 3.0 and later

In ASP.NET Core 3.0 and later, there are two new kinds of middleware element, and they are called UseRouting and UseEndpoints:

public void Configure(IApplicationBuilder app, 
  IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    app.UseRouting();
    app.UseEndpoints(endpoints =>
    {
        endpoints.MapGet("/", async context =>
        {
           await context.Response.WriteAsync("Hello 
                           ...