Season the pork: Combine the dry ingredients in a bowl. Toss the pork thoroughly with the seasoning until evenly coated.
Sear the pork: Set the Instant Pot to Sauté. Brown the pork pieces on all sides to develop color and flavor.
Pour in the chicken broth (or apple juice) and vinegar. Add liquid smoke, if using.
Seal and cook on High Pressure for 75 minutes. Allow a 15-minute natural release.
Remove the pork and shred. If the cooking liquid is thin, reduce it using Sauté mode. Fold the concentrated juices back into the meat.
While the pressure on the Instant Pot is releasing, bring a large pot of salted water to a boil and cook the pasta according to package directions. Drain.
While the pasta is boiling, in a medium saucepan, melt the butter over medium heat. Whisk in the flour and cook for about 1 minute, until the raw flour aroma dissipates.
Gradually whisk in the milk. Simmer, stirring frequently, until the sauce thickens.
Remove from heat. Stir in the cheese, salt, and seasonings until smooth and fully incorporated. Fold in the cooked pasta.
(Optional) Melt 2 tbsp of butter in separate saucepan over medium heat. Add panko breadcrumbs and stir until crumbs are golden brown and crisp. Lightly season with salt.
Spoon mac and cheese into bowls and top with warm pulled pork (and breadcrumbs, if using). Drizzle with reserved cooking juices or barbecue sauce if desired, and serve immediately.