Season the chops with the salt and pepper and dredge them in 1/4 cup flour, shaking off the excess.
Brown the chops in two batches in the oil over medium-high heat, 3 minutes per side, then stack them loosely in a 6-quart slow cooker.
Cook the onions in the skillet until golden, 8 minutes, then add the garlic for 30 seconds.
Stir in the remaining 1/4 cup flour for 1 minute, then gradually whisk in the broth and Worcestershire.
Pour the onion gravy over the chops, sprinkle in the thyme and cover.
Cook on low until the pork reaches at least 145°F and is tender but sliceable, 4 1/2 to 5 hours.
Rest the chops in the gravy for 5 minutes before serving.