The way I understand it ALL of your portfolio is counted, meaning that all capital gains are then taxed. So you are infecting your “private” portfolio. Which is rather unpleasant, because you don’t want to pay capital gain taxes on the long term stocks which you are not planning to sell. Note: I’m still not sure if my understanding is correct.
Yes, that could be classified as a violation of the employment contract. I don’t think the authorities will be notifying the employer though. This is an assumption though.
I guess it really comes down to the percentage of income you are generating with the option writing, plus the canton you live in. You might be classified as a professional trader in canton Schwyz for just writing options which generate 1k per year, while you are not classified in Zurich for writing options which generate 25k per year (while earning 100k).
I read a little bit more on the topic, and found the following article from NZZ in 2019: here (in German)
It mentions that canton Zürich only classified 100 private people in the previous 5 years (before 2019) as a professional trader. One reason for this: once you have professional trader status, you can also deduct losses from the profits.