Yes, the 20-part Learn HTML series has no article titled #Accessibility because accessibility isn't a separate topic.
The 20-article learn HTML is a 20-section series on learning HTML, which is accessible by default. Our job as developers is to not fuck that up! Teaching you how to not fuck up accessibility, and rather ensure accessibility, is covered in Every Single Section of the series because it is the core of HTML.
Turns out there might be a lot more to HTML than you might have thought. I learned (and shared) a ton of nuggets along the way, and diligently updated MDN in the process.