Diagonally opposite the right hand side of the entrance door is the TV background wall. If a gray mirror is used to decorate the TV background wall, will there be any Feng Shui taboos?

No, because it is not directly facing the door. Warm reminder: Depending on your apartment type, there is a suggestion to choose a direction for the kitchen stove, towards the window, otherwise it will be too close to the bathroom. Originally, the kitchen and bathroom are The fire and water are incompatible next to each other. It would be better if the stove is adjusted. Also, it is best to stagger the door of the bathroom and the door of the second bedroom. It would be easy to handle if it is not a load-bearing wall.