Is there any opinion on Feng Shui if the sofa is not against the wall?

No, there is no explanation. The sofa does not have to be placed against the wall. It can be placed anywhere according to the layout and beauty of the room. As long as it is convenient for you and does not hinder others, it is comfortable to sit on. That's it. In fact, there are not many things related to Feng Shui in life, so don’t associate everything with Feng Shui.