Set the Instant Pot to Sauté and add 1 teaspoon oil. When hot, add the minced garlic and stir for about 10 seconds until fragrant, then turn the Instant Pot off.
Add the broken fettuccine noodles to the pot and pour in 2 1/2 cups low-sodium chicken broth, making sure the noodles are submerged.
Close the lid and set the valve to Sealing. Cook on Manual/High pressure for 3 minutes.
When the cook time ends, allow a natural pressure release for 6 minutes, then carefully turn the valve to venting to release any remaining pressure and open the lid.
Stir the pasta, breaking up any pieces that are stuck together.
In a small bowl, whisk 1 cup milk with 3 teaspoons cornstarch until smooth. Add the milk mixture to the pasta along with 1/2 teaspoon onion powder, 1/2 teaspoon dried basil, 1/2 teaspoon dried parsley flakes, and 1 cup freshly grated Parmesan. Season with salt and pepper to taste.
Set the Instant Pot to Sauté and gently stir until the sauce just begins to thicken, then turn the pot off.
Let the pasta sit a few minutes off heat; the sauce will thicken as it cools. Add extra Parmesan if you want a thicker sauce before serving.