Pat pork chops dry and season both sides with salt, pepper, smoked paprika, and dried thyme.
(Optional) Heat oil in a skillet and sear pork chops 1–2 minutes per side until lightly browned; transfer to the crockpot.
Place half the sliced onions in the bottom of the slow cooker as a bed for the chops.
Arrange pork chops over the onion layer and scatter remaining onions on top.
In a bowl, whisk together chicken broth, apple juice, Worcestershire sauce, Dijon mustard, and minced garlic.
Pour the liquid mixture evenly over the pork chops and onions in the crockpot.
Cover and cook on LOW for 6–8 hours or on HIGH for 4 hours, until pork reaches 145°F and is tender.
Remove the chops to a plate and tent with foil to rest while you finish the gravy.
If desired, mix cornstarch with cold water and stir into the crockpot juices; cook on HIGH for 10–15 minutes or simmer in a saucepan until thickened.
Return chops to the sauce to coat or spoon the gravy and onions over each serving before plating.