The article nicely explains how to build a minimalist OS — works great as an intro material. I think understanding basic OS concepts is essential for performance tuning and debugging.
When I learned OS, I followed MIT 6.828 (https://pdos.csail.mit.edu/6.828/2017/overview.html) and implemented a small OS called JOS based on Xv6. So if you're looking for some teaching OS in x86, check it out.