This issue frustrates me so much as well. I’ve found a workaround that works most of the time, which is to say something along the lines of:
Please do not use em dashes. If you must include them in your revision summaries (the part at the end explaining what you did), you may, but NOT in any of the work I will be presenting.
This has worked for me so far, you might have to keep reminding ChatGPT every now and again though.
I hope this helps!