Place water and trivet inside pressure cooker.
Score ham by making small cuts in the skin of the ham, 1-inch apart.
Attach pineapples to outside of ham with toothpicks and press cloves on outside of ham.
Create boat with a double layer of foil and place ham inside of foil boat.
Lower ham into instant pot.
Mix together pineapple juice, brown sugar, and maple syrup. Pour over ham.
Crimp edges of foil to seal.
Close lid and set pressure release valve to sealing.
Press manual or pressure cook button and set to 18 minutes.
Natural pressure release.
Carefully remove ham (still wrapped in foil) from instant pot.
Remove trivet and pour out water.
Pour the juices from inside the foil boat to instant pot.
Set ham aside to rest.
Whisk together 1/4 cup cold water and 1 teaspoon corn starch.
Mix cornstarch slurry into juices in instant pot.
Press sautte button and bring glaze to a boil. Let boil, 5 minutes, until thickened.
Remove pineapple and cloves from ham.
Pour glaze over ham and serve with pineapple slices.