If you came here to point out how content negotiation isn't a "trick" but rather a simple basic part of the core protocol: think first on the fact that there was once a time when you didn't know that.
I mean, I also once didn’t know how to program, doesn’t make programming a trick. As another comments pointed out, it’s worthy of an article. But a trick is a weird description for it. It’s like saying it’s a trick that you can do `console.log` and it will output it in the browser console.
If we can all agree it's an interesting topic of discussion, we can set aside debating the semantics of whether it is a "trick" and let the author express themselves using the words of their choosing. Policing the definition of trick is surely not curious conversation.
I disagree that this is a clickbait title. I also disagree that those complaints are worth discussing. The guidelines specifically discourage us from complaining about things "too common to be interesting." And the articles that I'd describe as clickbait are simply too low quality to be posted anyhow. ("Clickbait", in my mind, is when the article uses provocative language to build expectations that it doesn't or can't deliver upon. "Trick" in this sense pretty clearly means, "here's a tool you can use to serve different content types to different user agents," and it delivers on that.)
These are really stylistic complaints; the author expressed themselves in a way that's not to your taste. Your tastes are valid, but there should be no expectation that every or any article will cater to them, and their not doing so isn't a criticism of the article and isn't something we can really have a productive discussion about in this medium. I find people use the term "clickbait" to try and reframe their tastes as something more objective.
Being old enough that I probably studied the http protocol before actually using it, by the time I encountered this functionality in the wild I already knew how it worked. So, no, there was never such a time.
