E-bike displays are designed to withstand rain or wash-downs. If the display is not damaged, no water should get in. But no display is 100% waterproof or airtight.
Cable openings and USB charging ports are places where air or water can still get into a display. Therefore, never point a hose directly at the display, especially not from below. But even if you haven't been riding your bike in the rain, you may occasionally get a fog spot in the middle of the display cover, especially if you leave the display in the sun for a short period of time. This is a normal reaction to the air trapped in the case. In most cases, the weather was previously wet, meaning the humidity was higher (>70% humidity). Even if the bike is stored in a dry but cold environment, this moist air can be sucked into the display. As soon as it is exposed to sunlight, which heats the air within a few minutes, the trapped moisture can no longer escape from the entry points quickly enough and condenses at the “highest” point of the windshield. This effect can be annoying, but in no case will it damage the electronics or impair their functionality. The amount of water bound in this small volume of air is extremely small and can never cause damage. To reduce trapped moisture, it's best to simply expose the display to direct sunlight for an hour or more - the heated air will eventually push the moisture out of the case.
Only if there are droplets inside the display cover should you contact your dealer, as this indicates a possible sealing failure.