Pat the chicken thighs dry with a paper towel and sprinkle all over with 1 tablespoon of the ranch seasoning mix.
Add the penne to a 6-quart Instant Pot with 4 cups water. Place the chicken thighs on top of the penne. Lock the lid and set to pressure cook on high for 8 minutes.
After the pressure-cook cycle completes, perform a quick release per the manufacturer's guide and wait until fully complete. Carefully unlock and remove the lid, watching for remaining steam. Transfer the chicken to a cutting board until cool enough to handle.
Meanwhile, combine the cream cheese, sour cream, Cheddar, and remaining seasoning mix (about 2 tablespoons) in a large bowl. Set aside.
Roughly chop the chicken into small pieces while still warm, confirming it is opaque throughout with no pink remaining and has reached 165°F. Stir the chicken into the cream cheese mixture, then add it to the pasta and stir until the cheese melts and the pasta is well coated.
Notes
Source recipe gives Total time as 40 minutes and Active time as 10 minutes, without a separate prep/cook breakdown; adjust as needed after your own testing. Requires a 6-quart Instant Pot multi-cooker; settings may vary by model. Refrigerate leftovers in an airtight container for up to 3 days; add a splash of milk or water when reheating. Freezing is not recommended, as the cream cheese sauce can separate after thawing.
Keyword creamy ranch pasta, dinner recipe, instant pot ranch chicken pasta, one pot pasta