Place chopped onion, garlic, corn cob pieces, sausage chunks, seasoning, and water or beer into a large resealable freezer bag. Remove excess air and seal.
Put the shrimp in a medium freezer bag. Remove air and seal. Staple above the seal to the large bag.
Take the bags out of the freezer to thaw.
Place the oil in the Instant Pot.
Dump the contents of the large bag in. Add the potatoes.
Secure the lid and select the manual setting for 9 minutes.
Do the quick release.
Add the shrimp and cook for another minute on the manual setting.
Place the oil in the Instant Pot and set to the sauté setting.
Once the oil is hot, add the diced onion and cook for two minutes.
Stir in the garlic and cook for one minute before turning off the Instant Pot.
Add the sausages, followed by the potatoes and corn.
Sprinkle in the Old Bay seasoning and the water or beer.
Secure the lid and select the manual setting for 8 minutes. Quick-release.
Add the shrimp and cook for an additional minute on the manual setting. Quick-release.