Turn on a multi-functional pressure cooker (such as Instant Pot), and select Saute function. Add butter, onion, and salt. Cook until onions are soft and caramelized, about 8 minutes. Close and lock the lid. Select Manual; set timer for 5 minutes. Allow 5 minutes for pressure to build.
Release pressure using the natural-release method according to manufacturer's instructions, 10 to 40 minutes.
Select Saute function again and cook for 5 minutes or until liquid has evaporated. Turn pressure cooker off and allow to cool for 5 minutes.
Combine cream cheese, sour cream, Worcestershire sauce, parsley, and garlic powder in a large bowl. Remove onions from pressure cooker using a slotted spoon and add to bowl with cream cheese mixture. Stir. Cover dip with plastic wrap and refrigerate for a minimum of 1 hour.