(My first post here: I’m a retired EE but only a month into 3D printing)
I found myself buying PETG filaments from Polymaker and Creality as I couldn’t get the right colors from BL or now not at all anymore. This set me into the whole filament calibration adventure using Bambu Studio.
Most of the posts on this subject are outdated and not relevant anymore. This actually made it much more difficult as I sometimes assumed information from posts was correct and current, while the issue has long since been addressed. Hopefully others find this subject before the older ones 
BS now allows manual profiles for pressure advance settings. Why these aren’t in the filament profiles is something I don’t understand but at least it isn’t necessary to do a calibration to set a value anymore.
Next is the Custom filament profiles. I found it’s best to select you can’t find the manufacturer and enter it yourself, starting with your name so that these get grouped and can be edited freely. For the new PETG profiles I used the generic as the base template. You then choose for which nozzles you want to create profiles… only select the one you’re working with and add others later when you have that nozzle installed.
I found good PETG settings here on the forum, with nozzle temperature of 265 C where the manufacturers suggest a maximum of 240 degrees. This also set me in the wrong direction by following manufacturer recommendations. Those must be seen in the context of the old slow printers, not for a fast Bambu Lab printer.
I hope this thread becomes the one that poos up when people search for this so that they don’t have the slow path I had to