Heat the Instant Pot on saute mode. Add the cooking oil. Once hot, add the carrot, celery, and onion until softened, about 3 minutes.
Add the beef and pork and saute for 8 minutes, breaking it up as it browns.
Turn off saute mode.
Pour in the white wine and deglaze the pan. Cook for 1 minute to burn off alcohol.
Pour in the chicken stock.
Break the spaghetti in half and set it over the top of the meat. Try to submerge the pasta in the water, without stirring.
Pour the tomato sauce over the top. Do not stir.
Secure the lid and set the vent to sealing (if necessary for your model).
Set to cook on high pressure for 8 minutes. When the time is up, carefully release the pressure. Remove the lid and stir.
Add the milk and season with salt and pepper, to taste.
Let rest until the sauce is to your desired thickness.
Serve with freshly grated Parmesan cheese.