Turn on the instant pot to the sauté option.
Add butter and olive oil.
When butter melts add cubed chicken and cook until no longer pink.
Add chopped onions and cook for 2 minutes.
Add garlic and continue to sauté for another 30 seconds.
Season with salt, pepper and oregano.
Add diced potatoes and carrots, cook for one minute.
Sprinkle flour on top and cook for another minute.
Cancel the sauté option, pour in the chicken stock, put the lid on and pressure cook on high for 3 minutes.
Do a manual release in bursts so it will not splatter all over the counter.
With a potato masher or an immersion blender blend part or all the potatoes, it depends on how chunky you want your soup to be.
Dissolve the sour cream in some of the milk and add to the pot.
Pour in the rest of the milk and press on the sauté option again to reheat the pot for another 5 minutes.
Turn the instant pot off mix in the cheese until it melts and spoon into bowls.
Garnish with more sour cream, bacon, diced green onions.