This is a 42 minute presentation that covers the basics of using R Markdown to produce PowerPoint files. It touches on another couple of RStudio products: R Studio Connect and Shiny. This covers a lot of customizations issues. Also see Rendering PowerPoint Presentations with RStudio.
Nathan Stephens. Make PowerPoint Presentations with R Markdown. RStudio Webinars, November 30, 2018. Available in html format.