Set the spaghetti noodles in the pot. Add the broth and 2 tablespoons of butter. Make sure the pasta is completely submerged.
Lock on the lid and set the vent to sealing. Pressure cook on high for 4 minutes. When done, do a quick release (be careful when venting as this is a starchy pasta).
With “Keep Warm” still on, add the shrimp to the Instant Pot. Close the lid. Leave for 4 minutes to cook the shrimp.
Open the lid and stir the pasta and shrimp. Add in the salt, pepper, lemon juice, remaining butter, garlic and Parmesan cheese. Stir to combine.
Allow the pasta to sit in the Instant Pot on Keep Warm for a few minutes to soak up the liquid and thicken.