Hit the saute button on the Instant Pot. Melt the butter, then add the onion. Cook until the onion is translucent.
Whisk in the flour and cook for 1 minute.
Whisk in 1 1/2 cups chicken broth and cook until thickened.
Add in remaining ingredients, except half and half.
Set manual cook time to 10 minutes. Let the pressure release for 5 minutes, then release remaining pressure.
Hit the saute button and stir in the half and half. Warm until heated through, but do not boil. If the soup gets close to boiling, remove the pot from the Instant Pot.