The Instant Pot is routinely used for making Greek Yogurt and collecting the resulting whey. The best luck has been with 1/2 gallons of milk and the medium temperature setting. Spotty results when doing a whole gallon at a time. Maybe the heat doesn't get through the milk evenly or the starter culture doesn't stay mixed in well. Getting the starting culture mixed in well seems to be important for the outcome. Insufficient mixing leads to clumps of setup yogurt and takes longer for the rest to setup. To get the culture mixed in well, use a hand mixer on low with only one of the beaters installed. Work it back and forth to get all the clumps of starter well mixed in. Gives a more even set in less time. Using 2 T to 1/4 C of reserved starter it's usually done in less than 8 hrs.
The whey is collected and used mostly in bread products. Also used in smoothies and in soups. In breads, add a little more whey than the amount of water called for. The resulting doughs tend to be a bit firmer than when simply using water. Most of the whey goes into our sourdough boules. Adds nice flavor