Slice the two racks of 2 racks into 3 to 4 sections so they fit easily into the Instant Pot. Crucially, ensure the silver membrane is removed from the bone side.
Generously coat all sides of the rib pieces with the 3 tablespoons dry rub.
Pour the 1 cup Root Beer into the bottom of the Instant Pot liner.
Place the metal trivet (or steamer rack) into the pot. Arrange the ribs on top of the trivet, standing them up vertically if necessary.
Secure the lid and set the valve to Sealing. Pressure cook on Manual/High Pressure for 23 minutes.
Once cooking is complete, let the pressure release naturally (NPR) for 10 minutes. Then, manually switch the valve to Venting for a Quick Release (QR) of any remaining pressure.
Carefully transfer the tender ribs to a foil-lined baking sheet. Discard the liquid from the Instant Pot liner.
Return the inner pot to the Instant Pot. Add the 1 cup BBQ Sauce, ½ cup packed Brown Sugar, 1 tablespoon Worcestershire Sauce, and1 tablespoon Apple Cider Vinegar to the pot.
Press the Sauté button. Bring the sauce to a simmer, stirring frequently for about 3–5 minutes, until it is hot and slightly thickened into a sticky glaze. Press Cancel.
Preheat: Set your oven to Broil (High) and position a rack about 6-8 inches from the element.
Generously brush the top of the ribs with the root beer BBQ glaze.
Broil the ribs for 1–3 minutes until the glaze is bubbling, sticky, and slightly caramelized. Watch constantly to prevent burning!
Let them rest for a few minutes before slicing and enjoying.