Pour all of the cheese into one medium bowl. Using your hands, mix the cheese with the cornstarch until the cheese is evenly coated.
Pour the wine, minced garlic, and lemon juice into your Instant Pot. Set the Instant Pot to the sauté function on the normal setting. Stir the ingredients to combine them.
When the wine mixture is hot, add the cheese mixture. Allow the cheese to melt, and then stir in the mustard and nutmeg.
Use the sauté function to keep the fondue hot enough for dipping. Turn the sauté function on and off while serving this dish to keep the fondue from scorching.
Keeping the Instant Pot on the warm function instead of on the sauté function may prevent the fondue from staying at the right consistency for dipping.