Preheat Pressure Cooker: Heat up your Instant Pot by pressing "Sauté" button, then click "Adjust" button to go to "Sauté More" function. Wait until the indicator says "HOT".
Sauté Chicken Breast: Season one side of chicken breasts with kosher salt and ground black pepper. Add 1 tbsp olive oil in the inner pot. Place chicken breasts in the pot (seasoned side down), then season the other side with kosher salt and black pepper. Brown each side for about 1.5 minutes. Set aside chicken breast. Add minced garlic cloves and sauté until fragrant (~a minute). Pour sauteed minced garlic into a stainless steel bowl.
Deglaze: Pour 1/2 cup (125ml) unsalted chicken stock in Instant Pot. Deglaze by scrubbing all the flavorful brown bits off the bottom of the pot and mix them into the stock mixture.
Pressure Cook Pasta & Chicken Breasts: Add 1lb (454g) pasta and chicken breasts in Instant Pot. Pour in the remaining chicken stock. Try to submerge all the penne pasta in the chicken stock. Layer the stainless steel bowl with Alfredo sauce ingredients (except the cheese and seasoning) on the pasta in the Instant Pot. Close lid and pressure cook at High Pressure for 4 minutes + 4 minutes Quick Release. Release the remaining pressure. Open the lid carefully.
Make Alfredo Sauce: Remove stainless steel bowl and chicken breasts from the Instant Pot. Melt 1 oz (32g) finely grated Parmigiano-Reggiano cheese into the Alfredo sauce 1/3 at a time while mixing with a fork. Taste & season with kosher salt (about 3 pinches) and ground black pepper.
Mix in Spinach & Alfredo Sauce: Heat up the Instant Pot by pressing "Cancel" button, then "Sauté" button. Mix baby spinach and ¾ of the Alfredo sauce with the cooked pasta. Taste and season with kosher salt and ground black pepper.
Serve: Cut chicken breasts into slices, then add chicken slices on top of the serving plate of pasta. Then, drizzle the remaining Alfredo sauce onto the chicken pasta. Garnish with more Parmigiano-Reggiano cheese if desired. Serve immediately~