The engine gets damaged when water gets into the piston chamber i think. Water compresses less than air so important things bend or crack if the engine is running too long with water in it.
I wonder how electric cars fare with deep water.
The ground clearance for my EV is 7 inches. The manual specifies it can handle 18 inches of water.
I don't know if that's the point where water messes with the electronics, or a swift current would start to move it sideways.