Pat the pork chops dry and season all over with the kosher salt and black pepper.
Heat the olive oil in a large skillet over medium-high until shimmering, 2 minutes. Sear the pork chops until well browned, 3–4 minutes per side, then transfer to a plate; they will finish cooking in the sauce.
Reduce heat to medium. Add the shallot and cook, stirring, until translucent, 2–3 minutes. Add the apple slices and cook until just tender and lightly caramelized at the edges, 2–3 minutes. Stir in the garlic and thyme and cook until fragrant, 30 seconds.
Pour in the apple cider, scraping up browned bits. Stir in the chicken stock and Dijon mustard, bring to a boil, then simmer briskly until reduced by about half and lightly syrupy, 5–7 minutes.
Return the pork chops and any accumulated juices to the pan, nestling them into the sauce. Simmer, turning once, until the chops reach 145°F at the thickest part, 2–4 minutes.
Transfer the pork chops and apple mixture to plates. Off the heat, stir the apple cider vinegar into the sauce, then whisk in the butter until glossy.
Spoon the sauce over the pork chops. Sprinkle with the parsley and serve immediately.