Whisk 1/2 milk with the yogurt starter to completely dissolve.
Add sweetened condensed milk, if using, to the Instant Pot with 1 cup milk and whisk in completely to dissolve.
Add in the rest of the milk to the starter/milk mixture. Whisk completely.
Lock the lid on (Or use a glass lid, and don't worry about sealing the lid or not. It does not matter!)
Press the Yogurt button and ensure that it is on the NORMAL setting, NOT LESS or MORE. Use the plus and minus buttons to select a time. 7-10 hours is ideal. I do 8 hours for Fairlife milk and 10.5 hours for Costco 2% (it requires longer incubation or it will be watery). The longer you "incubate," or let it sit, the more tart it will be. Some people incubate up to 24 hours. The Instant Pot will start counting UP, not down like when pressure cooking.
After the 8-10 hours are up, take the liner out of the Instant Pot and cover with a lid, or plastic wrap, or foil. Refrigerate 8 hours, or overnight. Do not stir or disturb. The consistency after incubation will be almost exactly the consistency after refrigeration, so if it is not set enough for you, continue incubation for another couple hours.
If you would like a super thick consistency like greek yogurt, use a yogurt strainer and strain to your desired consistency after chilling.
After refrigeration, you can mix it up and transfer to a large storage container, individual containers, or mason jars.
Enjoy with your choice of sweetener, fruit, granola, etc.