There's still a physical button for the wipers. On the Cybertruck it's on the steering wheel. When you press it to wipe (generally used for spray-washing the windshield), the entire menu pops up where you can choose the speed, frequency, etc.
I discovered this by chance. And it seems to be subtly mentioned in the manual.
https://www.tesla.com/ownersmanual/modely/en_us/GUID-A5C33F3....