V2.0 is version with Sensirion SDP31
Sensor adress is 0x21 or 0x22.
Adress uses in air module is 0x21 - connect ADDR to GND with 0 Ohm
Adress for 02 flow sensor is 0x22 - connect ADDR to GND with 1.2 Ohm
0x21 ADDR connected to GND
0x22 ADDR connected with 1.2kOhm to GND
0x23 ADDR connected with 2.7kOhm to GND
V2.1 is version with alternative sensor from Würth Elektronik 2513130810401