The maximum amount of permitted NOx emissions during Real Driving Emissions tests depends on when the car was admitted. There are two types of relevant admissions:
Car types approved between September 2017 and December 2019 must meet the threshold of 168 mg/km, if the was first admitted before December 2020. Car types approved later, or cars that were first admitted in 2021 or later, must meet the threshold of 120 mg/km.
In the NOx bar of the RDE guiding view, the left red marking represents the 120 mg/km threshold, and the right marking shows the 168 mg/km threshold.
Source: German Wikipedia