When shooting objects in the glass window, a polarizer is often added in front of the lens to increase the intensity of the projected light. Why?

Because not only does light come out of the glass, but the glass also reflects the light outside. So when the two kinds of light are confused, you can't see clearly what you are shooting.

However, the polarization directions of transmitted light (refracted light) and reflected light are different, so adding a polarizer can filter out the reflected light, leaving only the transmitted light in the room and making the room see more clearly.