Sorry if it sounds rude, but have you used the web on the desktop in the past 10 years? Anything under 1000px-wide windows and sometimes 1200px-wide ones gets you the “mobile menu” on most websites. It’s a consequence of Bootstrap and other fixed-breakpoint frameworks. Overflow menus like what you see on GitHub repositories are the minority.
And for an example that does it better, legacy.reactjs.org :)
When I saw it I wondered how they managed to drop the ball so hard and how much they paid for it. All they needed is to expand and slightly restructure the docs, but apparently someone sold them a complete redesign that just made the whole docs way less usable (a11y aside, can't speak for that).
