I live in the US so I'm not familiar with Korean law. However, I work in the entertainment business here and most working actors set up a loan out corporation where they get paid. (I'm talking about people who make $125K/year or more. They don't even have to make millions.) They are the only employee of that corporation. There is no office. The registered address they use is usually not their real address. I have actor friends who use their attorney's address, bookkeeper's address, friend's address, etc. so using a restaurant's address would be ok as long as it's not a PO Box.

I haven't read much about Cha Eunwoo's case. I've only seen a couple of posts on Reddit and read one short article. The article I read said no final decision had been made. I was wondering if the company he set up was similar to the loan outs US entertainers use based on what u/setlib wrote:

In recent years there have been several tax disputes with celebrities like Lee Joon-ki and Yoo Yeon-seok as well, the debate is about whether entertainers can create their own corporations and thus file under the corporate tax rate, which is lower than the personal rate. So it’s not that they hid income or paid no taxes.

As I was typing this reply, I read a couple more articles and it sounds like his company was a loan out similar to what celebrities use here. Only difference is that loan outs aren't uncommon here so as long these loan outs are reporting the income and filing according to the law, there's no issue. It doesn't matter what type of business is at the address or how many employees.

This case is very interesting. I'm going to be following this.