From a Feng Shui perspective, is it okay to use a mirror on the door of the master bedroom bathroom?

Your idea is a good one and not a bad idea. But you should still pay attention to: the mirror cannot face the door of the room, because the mirror has a mirror god, and each door also has its own door god, so if the mirror faces the door, it will scare away the door god who usually protects us and let the contents of the room go away. It is easy to get stuck. People are most relaxed and unsuspecting when they are sleeping, so if you wake up in the middle of the night and are frightened by yourself in the mirror, it will hurt your soul. In addition, looking at the bed in the mirror can easily cause couples to fall out, increasing the possibility that the other half will often have an affair. Therefore, your bathroom door had better not face the bed! Once you know these key points, there won’t be much of a problem.