Seal the balcony, or hang something evil, but if you want to sell it, people who come to see the house will be more afraid, and sealing a balcony may also affect the transaction price, but sealing the balcony will at least increase the space.
Anyway, if you want to sell it, don't worry so much, wait for the buyer to come. Not everyone believes in Feng Shui, but if you don't believe in Feng Shui, or the buyer doesn't like chimneys, he just thinks that smoke will affect the environment.
It's purely a personal opinion, I just hope it's valuable to you.