Turn Instant Pot to saute setting. Once warm, add olive oil and breakfast sausage. Break up sausage with a wooden spoon and cook until no longer pink.
Meanwhile, whisk eggs, milk, salt and pepper. Set aside.
Add potatoes to the Instant Pot and cook for 2 minutes. Turn off saute setting. Dump everything out of the pot into a large bowl and spray the instant pot well with nonstick spray. At this point you have two options in cooking style. The first instructions have resulted in some burn results for some people. This method has worked for my Instant Pot but it seems like newer version are more sensitive. If you have a new version or want to be extra safe, follow the second method of cooking (still in the Instant Pot).
OPTION 1: Put sausage and potatoes back into the instant pot then pour egg mixture over the sausage and potatoes. Press down to make sure all the potatoes are covered. Top with the shredded cheese. Turn Instant Pot to manual high pressure and set for 25 minutes. Once done cooking, use the quick release method to release the steam.
OPTION 2: Spray a bowl or oven safe pan that will fit into the Instant Pot with nonstick spray. Add potatoes and sausage into the bowl. Pour the egg mixture over top of them. Top with shredded cheese. Add one cup of water to the Instant Pot and place the rack inside the pot. Place the prepared casserole on top of the rack. Put lid on Instant Pot and make sure the pressure valve is sealed. Cook on manual, high pressure for 25 minutes then quick release.