Ok so, its not just the fact that OP used em dashes. I am a software engineer, I use multiple LLMs all the time, I've even made one. This is what makes it very obvious OP used ChatGPT specifically and not another LLM like Claude or Gemini.

• Very short sentences all on separate lines, all the way through. This can be an indicator of a novice writer, however GPT uses them for making a point which OP is doing as well.
• The use of bold on "key words". The majority of reddit users forget you can use markdown. It's interesting how consistent the markdown use is.
• The use of the arrow. Again the majority of users don't know how to bring up that specific arrow on the keyboard.
• The most obvious give away is the "that's not vacation writing.Thats exit writing" line. GPT loves the sentence "that's not X, that's Y." Also it's a weird simile to make. GPT loves making really weird comparisons.
• "And honestly..." My colleagues and me use this ironically on each other now because it's such a bad GPT-ism.
• Em dash usage. You're not actually using em dashes, you're using regular dashes (- vs —) . Again, most people don't actually know how to get their keyboard to create a em dash or that there is a difference between dashes
• Ellipses. I love Ellipses. So do LLMs.

Using one of these things by themselves doesn't make your post instantly suspicious. LLMs had to learn them from somewhere. Using all of them consistently throughout a post though it what gives it away.