Heat milk to 180° F in instant pot using sauté function. Whisk now and then to prevent burning.
When milk reaches 180° F, turn off pot and allow the milk to cool to 110° F. Remove the liner from the appliance to speed the cooling if you want.
When the milk is 110° F, whisk in the yogurt.
Cover pot. Select "yogurt" function on instant pot and set to 24 hours, or desired time for yogurt to culture.
After 24 hours, remove lid from yogurt. Stir yogurt (it may develop a cream top that you can mix back in) and scoop into storage jars if not straining.
If you want to strain the yogurt, chill thoroughly first. Set a colander in a large bowl, line with flour sack towel, several layers of cheesecloth, or something similar, and scoop all the yogurt into the towel.
Twist the towel over the yogurt to protect it from anything that may land in it, and let the whey drip out until the yogurt reaches desired consistency.
Store yogurt in jars. Eat within a week or two. Reserve whey for other uses.