Is the WH-1000XM4 waterproof? Can I use it in the rain or while sweating?

The unit is not waterproof. If water or foreign objects enter the unit, it may result in fire or electric shock, and you should stop use immediately and consult your nearest Sony dealer. You should be especially careful when using it around sinks, in rain or snow, in humid locations, or while sweaty. Never insert the USB plug when the unit or charging cable is wet, as a short circuit may occur. (Page 1)