Set the Instant Pot to Sauté and add 1 teaspoon oil. When hot, add the minced garlic and stir for about 10 seconds, then turn the Instant Pot off.
Add the broken fettuccine and pour in 2 1/2 cups low-sodium chicken (or vegetable) broth, ensuring the noodles are submerged.
Secure the lid and set the valve to Sealed. 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 to separate any clumps and loosen the noodles from the bottom.
In a small bowl whisk together 1 cup milk and 3 teaspoons cornstarch until smooth. Add the milk mixture to the pot along with 1/2 teaspoon onion powder, 1/2 teaspoon dried basil, 1/2 teaspoon dried parsley, and the grated Parmesan. Season with salt and pepper to taste.
Turn the Instant Pot to Sauté and cook, stirring gently, until the sauce just begins to thicken. Turn the Instant Pot off.
Let the pasta rest a few minutes—the sauce will thicken as it cools—then serve. Add extra Parmesan if a thicker sauce is desired.