For that soup, you could also use some fresh mushrooms. A few herbs and spices would also be welcome. Anyway, it's going to be a delicious dish.
Put the instant pot in browning mode
Brown the onions in the butter 2 min
Add the frozen mushrooms
Stir until the thawing water has evaporated a little
Add the cornstarch, broth, and, pepper
Switch to pressure cooking 8min
At the end of the cooking mix everything with the cream
Servings 4