Make sure that your stainless steel insert is in your Instant Pot. Press "saute" setting and wait 2 minutes.
Add oil and butter to your Instant Pot and let it melt.
Cut each chicken breast lengthwise, to make two cutlets. Season with salt and pepper and dredge in flour.
Brown each chicken cutlet on each side. Remove onto a plate.
Add more butter to the Instant Pot. Add garlic, onion and mushrooms and saute until fragrant, about 3 minutes.
Press "cancel/off" button. Add chicken stock and wine to vegetables. Stir well.
Place chicken in the sauce. Close the lid, set valve to "sealing" positions (the newer IP models do it on their own).
Make sure the IP is set to cook at HIGH pressure. Set timer to 7 minutes.
The IP will beep and it will start coming to pressure. That can take about 5 minutes.
Once the timer is done, press "cancel/off" button and let the Instant Pot release pressure naturally.
Once the pressure pin drops, carefully open the lid away from your face.
Remove the chicken and set on a plate.
Mix cornstarch with water and add to the sauce. Stir and let it sit for a few minutes to thicken.
Serve chicken with sauce over mashed potatoes, roasted potatoes, rice or noodles.