Heat your Instant Pot on Sauté, and once it's hot, add oil. Place poblano strips in a single layers as much as possible and allow them to char. Flip only occasionally, and cook for about 10 minutes.
Add butter and when it melts, add in onions and garlic and cook along with the peppers until soft, about 2-3 minutes
Add all other ingredients except crema, close the Instant Pot and set for 2 mins at Low Pressure. When it is done, release pressure quickly.
Add in crema while stirring so that it incorporates into the sauce.