I don’t think it’s just the humidity, high temperatures/uncalibrated pressure advance (or firmware equivalent)/uncalibrated retractions can surely lead to excessive stringing as well. But in my experience with PETG, if you leave it exposed to humid air for a while, it will pull string no matter your calibration, and also leave tiny blobs on corners of your print. In general, I’m not a big fan of the material 🤷‍♂️