Set your Instant Pot to "Sauté" mode. Once hot, add olive oil. Add the cubed chicken breast and cook for 3-4 minutes, stirring occasionally, until lightly browned on all sides. It doesn't need to be fully cooked through at this stage.

Add the minced garlic to the pot and cook for another 30 seconds until fragrant, being careful not to burn it. Press "Cancel" to turn off the Sauté mode.

Pour in the chicken broth, scraping the bottom of the pot with a wooden spoon or silicone spatula to deglaze and release any browned bits. This prevents a "Burn" error.

Evenly lay the broken fettuccine pasta in a crisscross pattern over the chicken and broth. Do not stir. Ensure most of the pasta is submerged in the liquid. If needed, gently push it down without stirring.

Secure the lid on the Instant Pot and make sure the sealing valve is in the "Sealing" position. Select "Pressure Cook" (or Manual) on High pressure for 6 minutes.

Once the cooking cycle is complete, carefully perform a Quick Release (QR) by turning the sealing valve to the "Venting" position. Be cautious of the hot steam. Once the float valve drops, you can safely open the lid.

Stir the pasta and chicken. It might look a little soupy at first, but the sauce will thicken. Add the heavy cream, freshly grated Parmesan cheese, salt, and black pepper. Stir gently until the cheese is fully melted and the sauce is smooth and creamy. The residual heat will continue to thicken the sauce.

Taste and adjust seasonings as needed. If desired, garnish with fresh chopped parsley before serving immediately. The sauce will continue to thicken upon standing.