Design is how it works, not how it looks. This article seems to mainly be talking about the "polish" of a design. There are more important principles which don't have anything to do with polish, such as not putting the Cancel button next to the Ok button.
More like this:
https://lawsofux.com
https://asktog.com/atc/principles-of-interaction-design/
https://www.nngroup.com/articles
I recommend prototyping the flow/feel of the app before working on the polish, or the functionality:
https://principle.app/