Xiao Wei saw plumes of "white gas" rising from the top of the jar. What are these "white gases" and how are they formed?

It's water, to be exact, a small drop of water vapor liquefied by cold.

Specifically, it is formed as follows:

When the pot is heated, the water in the pot will boil, and then the water vapor will enter the air from the pot (high temperature) (low temperature). When water vapor is liquefied by cold in the air, it will form droplets, which are liquid in nature.

Water vapor is colorless, odorless and invisible to the naked eye, including the gas that comes out of the mouth when it is cold in winter, and also the small liquid droplets that liquefy when it is cold.

I hope my answer is helpful to you.