I think you are confused about what the IRS considers a business or not.
The IRS has written on this issue regarding a person who makes investments for a living with Topic No. 429 Traders in Securities (Information for Form 1040 Filers) which classifies individuals as: Investors, Traders, and Dealers. Skipping Dealers as they have obvious customers,
So an ...
You may be able to deduct some of it. However, it is limited to the portion of the apartment that is used exclusively for work.