What are you trying to do? I presume the subject is a question, but using "<iframe> content in a yaml file" doesn’t make sense to me. YAML is a text format, so I think you mean you want to embed an iframe in a content file.
If that is the case, build a shortcode. There are other ways to do it, but that will work and teach you how.
It was good to share your repo, but your repo doesn’t have content or layouts, so it won’t actually be useful to assist you. 