Why do electrical appliances short-circuit when the weather is humid?

The water in humid air is not pure water (it may contain some ions and inorganic weak acids such as carbonic acid - CO2 in the air dissolves into water vapor)

When water vapor in the air encounters Electrical appliances (temperature is generally below 100 degrees Celsius) will liquefy

And water with impurities is conductive. When such liquefied water reaches the copper-plated circuit of the printed circuit board of the electrical appliance (the circuit is often exposed and dense), it will cause loops to form in places that should not form loops (that is, short circuits)