Waymo and Cruise are both geo-fenced systems. Ergo, they only work in areas that have been precisely mapped and programmed for the particular area. Their sensor suite is composed of Radar,  Lidar, and cameras. Cruise got caught with their fingers in the cookie jar lately, as they claimed full autonomy but behind the scenes, a team of remote operators was watching the cameras and remotely driving the car.
I believe they are coded with a bunch of If, Then, Else branches in C++. Tesla fought it out with such code for several years. Last year, Musk scrapped the complete software for FSD and went to a Machine learning neural net. The latest system teaches the car how to drive by learning from a team of elite drivers driving a car. Also, the Tesla system is not geo-fenced. It works anywhere there is a road. I seriously doubt that any autonomous car had ever been on my stretch of gravel road before today. I set my destination in my yard and the car was happy to drive down the road with no striping of any sort. It did OK but I prefer to stick closer to the paths in the gravel that have very little loose gravel. The car was not as fussy, so I disengaged it. It has a way to go, IMHO on gravel paths. Does better on paved, with striping.