Select SAUTE on your Instant Pot and set to the Normal setting and add the oil.
Once hot, add the pancetta and cook until beginning to crisp and the fat has rendered, about 6 minutes.
Transfer to a paper towel-lined plate and set aside.
Meanwhile, pat the chicken dry with paper towels and then season all over with the thyme and salt and pepper.
Working in batches, place the chicken, skin side down, into the pot and cook for 4 minutes and then flip and cook for another 4 minutes, or until nicely browned. Don't overcrowd the pan!
Transfer the seared chicken to a rimmed baking sheet.
Add the sliced leek with a 1/4 teaspoon salt to the pot and cook until soft, about 3 minutes.
Hit CANCEL and then add the wine. Now, hit SAUTE again, but now set it on More (this is done by pressing the SAUTE button until you see More).
As soon as the liquid comes to a boil, hit CANCEL and then select SAUTE again, and then set it back to Normal. Simmer for 5 minutes and then hit CANCEL.
Add the pancetta, potatoes, mushrooms, and chicken to the pot.
Secure the lid into place and then select MANUAL or PRESSURE COOK at High Pressure for 8 minutes.
Once cooking is complete, release the pressure by using a Quick Release.
Carefully remove the chicken and place on platter with the vegetables and some of the sauce poured over the top.
Garnish with chopped parsley and serve with remaining sauce on the side.