The most puzzling AI-ism to me is probably the "Not x. Not y. But z."
Not the em-dashes (an essential piece of punctuation). Not "That isn't x, it's y" (a useful if inelegant way to clarify an argument). But consecutive examples of what your subject isn't -- conveyed in fragmentary, staccato sentences -- before a declaration of what it is.
Feel like this is an inherently irritating rhetorical device. And I don't recall regularly coming across it in pre-AI writing. So, I don't understand why LLMs are so in love with the template