"Apparently Volkswagen/Audi cheated on the USA emissions tests since
2009 to 2015 by turning off the EGR to lower nitrogen oxide emissions
ONLY when the car was being tested for emissions. "

THAT IS NOT HOW IT WORKS.

When there is not enough exhaust gas recirculation (EGR) there are more oxides or nitrogen produced because of the higher peak combustion temperature. The EGR valve, by lettting in exhaust which is oxygen starved atmosphere, lowers the burning tmperature of the mixture, and thus "burns" less nirogen into N2O.

You had it backwards.