Thanks for your response.
ngx-formly is awesome. I wrote an article to build dynamic form in Angular 9 and Ivy without using any library (https://medium.com/weekly-webtips/tech-building-dynamic-form-in-angular-9-and-ivy-intro-96e6d12c39be) so check it out.
The reason we don't want to use third party library is because sometimes form can be so complex and varied across organizations. Also I want my readers to know that building dynamic form is not some magical things that only experts can do. They can be able to create dynamic form from scratch and customize as much as they can.