Integration tests with WebApplicationFactory in dotnet6

I have a class public class CustomWebApplicationFactory : WebApplicationFactory<Startup> that have a method

protected override IHostBuilder CreateHostBuilder()
    {
        return base.CreateHostBuilder().UseEnvironment("Development").UseLogDefaults();
    }

After deleting from Program.cs this code

public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .UseServiceProviderFactory(new AutofacServiceProviderFactory())
                .ConfigureAppConfiguration((context, config) =>
                {
                    var builtConfig = config.Build();
                    /*code here*/
                })
                .ConfigureWebHostDefaults(webBuilder => { webBuilder.UseStartup<Startup>(); });

The CreateHostBuilder method started to throw a null reference exception. If I delete CreateHostBuilder override method then in tests appears an exception The entry point exited without ever building an IHost.

Moving the code from Program to CreateHostBuilder did not help. Startup class is untoched, only deleting IHostBuilder CreateHostBuilder causes the error