Set Instant Pot to Saute. Once the IP is hot, melt the butter or add oil instead.
Add the ground beef, let it cook without moving for about 1 minute, to get a nice sear on it. After that, break it up using a wooden spoon as it cooks.
Once the ground beef has browned, add salt, pepper, and Worcestershire sauce. Stir to combine. Add onion, garlic, green pepper, and mushrooms. Stir and cook for another 1-2 minutes.
Add the ketchup and beef broth. Stir to combine. Scrape the bottom of the pot with a wooded spoon, to make sure bits are not stuck to it.
Add pasta and gently stir to combine just enough to submerge it into the liquid.
Cover and seal the lid. Make sure the valve points to Sealed. Change the setting to manual and adjust the time to 5 minutes on High Pressure.
Once Instant Pot beeps to show that it's done, do a quick release, by changing the position of the valve to Vent. Carefully remove cover and stir.
Turn off the Instant Pot.
If using sour cream and cream cheese, click on Saute, add them to the pot, stir and cook until melted and creamy. Taste and adjust for salt and pepper. Turn off the Instant Pot after that.
Top with cheese and put the lid back on but don't seal. Allow a minute or two for the cheese to start to melt. Stir to combine.