If necessary, remove sausage from casings.
Turn on the "Saute" setting on the Instant Pot, and add onion, sausage, and Italian seasoning to inner pot. Cook for about 5-6 minutes until onion is softened and sausage is browned and no longer pink. Drain mixture if there is more than 2-3 tablespoons of grease.
Add pasta to pot in an even layer on top of the sausage mixture, and cover pasta with beef broth.
Without stirring(!), add marinara or spaghetti sauce on top of the pasta. (Not stirring in the tomato sauce will prevent receiving the "Burn" notice on the Instant Pot.)
Close the instant pot with the lid, and turn the steam valve to "Sealing".
On the Instant Pot, click "Cancel" (or equivalent) to stop "Saute". Click the "Manual" button on High Pressure. Set the timer for 5 minutes* and allow the Instant Pot to come to pressure (about 10-15 minutes).
Turn the steam valve to "Venting" to release the pressure manually.
Stir in cottage cheese (or ricotta) and mozzarella cheese.
If desired, top with Parmesan cheese and parsley. Serve hot!