I'm pretty sure that you're thinking of Cruise not Waymo. They released info last year that they very frequently had to step in, but that the ratio was still 1 operator per 15-20 fleet vehicles. https://www.cnbc.com/2023/11/06/cruise-confirms-robotaxis-rely-on-human-assistance-every-4-to-5-miles.html

Waymo does have support operators, but I can find no reference to how many they have in comparison to their vehicles.