Comment from@ajrgodfrey about the Rmd template:

It leads to a nice reading experience, but the HTML does not actually fully meet WCAG with for example too many heading level 1 tags on pages (sections are<h1> and should be<h2>) so there is an opportunity to upgrade the template to the latest and best WCAG has to offer.

Ref:https://www.w3.org/WAI/WCAG22/Techniques/html/H69.html