Wanted to add to this thread for whoever finds it, the transfer case fluid in my 2017 Buick Envision 2.0T AWD was NOT factory filled with Auto Trak II/automatic transmission fluid like this thread suggests. Opened the fill plug and it smelled and looked like gear oil.
Called the Buick dealer, gave them the vin and they said it takes .69 quarts of AC Delco 19351882 10-4105 "GL-5 75W-90 Synthetic Power Transfer Unit (PTU) Lubricant". This fluid is around $100/quart from GM.
After some research, GL-5 75W-90 synthetic gear oil seems to be the replacement for this fluid, the dealership doesn't even keep this $100/quart fluid in stock. I was able to fit about .8 quarts to fill, used Pennzoil Platinum GL-5 75W-90.
The manual doesn't state what kind of fluid to use in the transfer case/rear differential of this car, I would suggest to call the dealer to confirm. My rear differential was slightly underfilled from factory like others have mentioned.