In automatic mode, different ppm level should result in higher fan speeds. That is at least the case with my filters. Cooking for example can be a trigger.
You are of course right that automatic mode does not do much. At the same time, higher fan speeds are noticeable (and annoying).
For my environment it never ramps up in that mode at all. Ambient levels are never higher than 10ppm or so.
I know the sensor works because once there was a small bin fire outside. There was no visible smoke indoors, I only noticed a slight smell. But the purifier immediately ramped up and showed over 200ppm.. So it does work.
I'm surprised it's so low as I live at the 2nd floor on a fairly busy street with many diesel buses passing.
You are of course right that automatic mode does not do much. At the same time, higher fan speeds are noticeable (and annoying).