Pat pork chops dry and season on both sides with salt, pepper, garlic powder, and any dried herbs; set aside.
Turn Instant Pot to Sauté. Add oil and butter. When hot, add garlic, onion (if using), and mushrooms. Cook, stirring, until mushrooms release their liquid and begin to brown.
Pour in white wine and deglaze, scraping up all browned bits from the bottom of the pot. Let simmer briefly to reduce slightly.
Stir in cream, chicken broth, thyme, and any remaining seasoning. Nestle pork chops into the liquid in a single layer, turning once to coat.
Lock lid, set valve to Sealing, and cook on High Pressure (Manual) for 8 minutes. Allow a short natural release, then carefully release remaining pressure.
While pork cooks, melt butter in a small saucepan. Whisk in flour and cook, whisking, until smooth and lightly bubbly. Remove from heat.
Transfer pork chops to a plate and tent with foil. Turn Instant Pot back to Sauté. Whisk roux into the hot cooking liquid until smooth. Simmer, whisking, until sauce thickens
Taste sauce and adjust with more salt, pepper, or herbs as needed. Return pork chops to the pot, turn to coat in sauce, and warm through for a few minutes before serving.