Add water and salt to the Instant Pot.
Pour in the elbow macaroni and stir gently.
Close the lid and set the valve to sealing.
Set the Instant Pot to manual mode for 4 minutes.
Once cooking is complete, perform a quick release of pressure.
Open the lid and stir the pasta.
Add butter and mix until melted.
Pour in the milk and stir well.
Gradually add the shredded cheddar cheese, mixing until fully melted.
If desired, sprinkle breadcrumbs on top before serving.