So if you punctuate correctly, you get accused of plagiarism, but if you don't, then you get penalised for incorrect punctuation... I suppose school is meant to prepare you for life, so it makes sense.
Plagiarism has a long history, and the options are numerous, including using some other student's prior work, or paying a human "homework mill" overseas to research write your report for you. It's usually the differential in styles that will get you noticed, because a teacher gets to know their students and what they're capable of in the classroom.
Also, using a hyphen instead of an em dash isn't "incorrect"; it's a traditional way of writing, because most of us grew up with ASCII, and only the one key on our keyboards. Only a journalism or literature class would be concerned with teaching the distinction and marking points for using those.
I could list about 5-6 signals of LLM generation that I've noticed. Proceeding to investigations and accusations is discretionary, and shouldn't be taken lightly.