It does not resembles that. It is usually grammatically correct writing, but it is also pretty ineffective writing bad writing with good gramar.
Let's grab a few books off the shelf (literally).
Douglas Adams' The Hitchhiker's Guide to the Galaxy has four emdashes on the very first page:
> It is also the story of a book, a book called THGTTG - not an Earth book, never...
Isaac Asimov's classic The Last Question: three emdashes on the first page (as printed in The Complete Stories, Volume I)
> ...they knew what lay behind the cold, clicking, flashing face -- miles and miles of face -- of that giant computer.
Mark Z. Danielewski, House of Leaves: Three emdashes on page 1
> Much like its subject, The Navidson Record itself is also uneasily contained -- whether by category or lection.
Robert Caro, Master of the Senate: Five emdashes on page one
> Its drab tan damask walls...were unrelieved by even a single touch of color -- no painting, no mural -- or, seemingly, by any other ornament
Other pages 1s:
* Murakami - 1Q84: 1
* Murray/Cox - Apollo: 1
* Meadows - Thinking in Systems: 1
* Dostoyevsky - The Brothers Karamazov (Pevear/Volokhonsky translation): 4
* Caro - The Power Broker: 5
* Hofstadter - Godel, Escher, Bach - 3
Honestly, when I started this post I expected to have to dig deeper than page 1. The emdash is an important part of English-language literature and I reject the claim that we should ignore all writing that contains it.
Secondarily, I think there's a part of the discourse missing: the presence of a syntactic emdash in a sentence on the internet is not itself a strong signal of LLM-writing - but the presence of an actual emdash glyph (—) should raise some eyebrows, esp. in fora that aren't commonly authored in rich text editors (here, twitter, ...)
(option-underscore, or option-shift-dash if you prefer to think of it that way)
On iOS, you can type it by simply holding down on the "dash" button then selecting the em-dash from the list of options it presents. It may also correct double-dash to em-dash a lot of the time, not sure.
I have used the correct em-dash everywhere I can for over a decade, which amounts to nearly everywhere.