This entire article is a a UX Myth and should be removed for spreading shoddily concluded info. This is a misapplication of Miller’s Law. Users don’t need to remember all the menu items to use them, they only need to recognize them, thus they can be longer than the amount of items we can remember. When is the last time you went to a website and tried to hold all the menu items in your head? You don’t, you usually are looking for the one menu item that suits your needs, and once you click on it, you disregard the rest, not trying to remember them at all.

Nielsen Norman article: “It’s a common misconception that limited short-term memory implies that menus should be similarly limited to 7 items. It’s fine to have longer menus (if needed), because users don’t have to memorize the full list of menu items. The entire idea of a menu is to rely on recognition rather than recall (one of the basic 10 heuristics for user interface design). There are many other usability issues in menu design, and shorter menus are certainly faster to scan. But if you make a menu too short, the choices become overly abstract and obscure.”

(https://www.nngroup.com/articles/short-term-memory-and-web-usability/)

UX Myths article: “Limiting the number of menu tabs or the number of items in a dropdown list to the George Miller’s magic number 7 is a false constraint. Miller’s original theory argues that people can keep no more than 7 (plus or minus 2) items in their short-term memory. On a webpage, however, the information is visually present, people don’t have to memorize anything and therefore can easily manage broader choices.”

(https://uxmyths.com/post/931925744/myth-23-choices-should-always-be-limited-to-seven)

There are about 9 other articles in the above link debunking the idea including one from Edward Tufte.

Tufte: “These studies on memorizing nonsense then led some interface designers to conclude that only 7 items belong on a list or a slide, a conclusion which can be sustained only by not reading the paper. In fact Miller’s paper neither states nor implies rules for the amount of information to be shown in a presentation.”

(https://www.edwardtufte.com/bboard/q-and-a-fetch-msg?msg_id=0000U6&topic_id=1)