Why isn't "on" (essentially meaning "one") not treated as singular even though meaning implies plural

These are good mind searching and expanding exercises!  I am impressed by the work that goes into their development.  If "on" really means "one" why is it not treated as singular even though meaning implies plural.  I know it's not good French but "Qu'es-ce qu'on va faire?" implies plural but is treated as singular ie not "vont faire".  (I remember my teacher getting really irritated with me when at the age of 9 I insisted that "on" was another way of saying "nous"!  Thank you in advance for your help and for curating such a good set of lessons.