Both the SGP30 and the BME680 have a big weakness that I experienced some years ago when I trying putting an air quality sensor together. They correlated the TVOC readings with the temperature. And sometimes it was bad, like a difference of just 1 or 2 degrees Celsius could double or triple the TVOC readings at the lower end of the scale (~50ppb), and add maybe ~50% at the upper end (~500ppb).

Are you seeing the same behavior?