Turn on a multi-functional pressure cooker (such as Instant Pot®) and select Saute function. Add olive oil and swirl to coat. Saute onion in the hot oil, 3 to 4 minutes. Add garlic and saute for 20 seconds. Pour in broth and scrape the bottom of the pot with a wooden spoon.

Layer sausage, mushrooms, cavatappi, Cajun seasoning, and tomatoes in the pot evenly in that order; do not stir. Close and lock the lid. Make sure the valve is set to Sealing. Select high pressure according to manufacturer's instructions; set timer for 4 minutes. Allow 10 to 15 minutes for pressure to build.

Release pressure carefully using the quick-release method according to manufacturer's instructions, about 5 minutes. Unlock and remove the lid.

Stir shrimp, cream cheese, and bell pepper into the pot. Close the lid and let sit on Warm setting to allow hot pasta to warm shrimp through, cook the pepper, and melt the cream cheese, about 5 minutes. Remove the lid and stir cream cheese to make sure it is incorporated. Stir in Parmesan cheese. Serve.