Hi,
I created a new project with the default blogdown configuration and got it to render with blogdown::serve(). Sort of--it doesn't slot it in the right date or give it the correct title.
My Rmd file was simply
---
title: "Video demo"
author: "Richard Careaga"
date: "12/21/2019"
output: html_document
---
<iframe width="560" height="315" src="https://www.youtube.com/embed/4SBjIkFNAGQ" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>)
It rendered to
---
title: "Video demo"
author: "Richard Careaga"
date: "12/21/2019"
output: html_document
---
<script src="/rmarkdown-libs/jquery/jquery.min.js"></script>
<script src="/rmarkdown-libs/elevate-section-attrs/elevate-section-attrs.js"></script>
<p><iframe width="560" height="315" src="https://www.youtube.com/embed/4SBjIkFNAGQ" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>)</p>
I haven't checked if it renders correctly on Netify!
So, the only thing I can suggest to to make sure the two scripts are where they should be in your directory and to replicate my experiment.