The fact that the character is not displayed in the mirror is described here Mirror Reflection Missing for Character on Medium Graphics Settings - #34 by n0mercygames and here Mirror Pixelation Issue / Bug? - #7 by redm .
But also the wall of the room opposite it is not displayed in the mirror if the wall hiding mode is enabled, which is not correct. Wall hiding should only work for the game camera, but right now it’s working for the world. In other words, the walls are not hidden from the game camera, but simply removed from the world as a game object.
I suggest using a layer mapping system for the camera, and the mirror will reflect everything.