I have migrated our application from .NET Core 2.2 to version 3.0. Actually I created the new application in 3.0 from scratch and then copied source code files. Everything looks
I also came across this issue while following the documentation https://docs.microsoft.com/en-us/aspnet/core/migration/22-to-30?view=aspnetcore-3.0&tabs=visual-studio
For your case I have checked and the code below will work, with the call to webBuilder.UseKestrel()
removed.
public static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.ConfigureWebHostDefaults(webBuilder =>
{
webBuilder.UseContentRoot(Directory.GetCurrentDirectory());
webBuilder.UseIISIntegration();
webBuilder.UseStartup();
});