I've been employing em-dashes extensively since I went on a JD Salinger binge circa 2002. Also, "incidentally", for the same reason. I use "Nb" a lot, from reading a bunch of DFW years ago. Oh, and that very-precise construction he does with "which" all the time, I stole that.
Before LLMs, I think em-dashes mostly signaled that you read books and paid attention to details, to the extent they signaled anything.