Place macaroni and salt in Instant Pot. Pour chicken broth over macaroni so that all macaroni is covered by liquid. Stir.
Cut butter into small pieces and place on top of pasta.
Place lid on top of Instant Pot and secure in place.
Move vent to SEALING position.
Press MANUAL button and set timer for 4 minutes.
When finished cooking, allow for a 10 minute NATURAL RELEASE, then move the venting to VENTING to quickly release the remaining pressure. (Some foam might come out of the vent, just use a paper towel to quickly wipe it off).
Remove lid and add whipping cream, milk, cheddar cheese, and Parmesan cheese. Add in seasonings and mix together until the cheese is all smooth and melted.