I still do not understand how the initial calibration of BSE680 for VOC, is done. Do you use a certain mix of gases (standardized mix), and measure the signal? Then double the concentration and check if the signal is doubled? Or is the calibratin done in accordance with some defined standard?
You have said that: "BME680 have no selection, so it is sensitive for almost all VOC component". But still i guess you need to calibrate it against something defined?
If an old sensor, calibration is performed automatically in the background if the sensor is exposed to clean and polluted air for approximately
30 minutes each.
If a new sensor in LP mode and there is a good variatioin in concentration, it take more than 8 hours to get the valid IAQ value. And if you want to compare between two sensors IAQ in the same background , it take more than 7 days for them to reach datasheet specification parameter setting 15+15%.
More information is presented in confidential documents, I don't share to you directly, maybe you need contact local FAE to get it under NDA.