Set Instant Pot to Sauté (normal/medium heat). Add the olive oil to the pot and swirl to coat.
Place the pork tenderloin directly into the bottom of the pot and cook, undisturbed, for 2-3 minutes. Cook all sides, repeating the process. With all sides browned, remove the pork to a plate and set aside.
Add the sliced onion to the pot and mix well. If necessary, deglaze the pan with a splash of dry white wine (or chicken broth) and continue to cook, stirring frequently, until onions start to soften.
Meanwhile, in a small bowl whisk together the garlic, chicken broth, balsamic vinegar, apple jelly, Italian seasoning, fresh minced rosemary, and salt. Add the garlic mixture and the apples to the onions and mix well to combine.
Transfer the pork back into the pot and securely lock the lid in place. Cancel the sauté function and set the steam release knob to the sealing position.
Select the Manual (Pressure Cooker) function and adjust the pressure to HIGH pressure (default). Set the timer to 5 minutes.
When the cooking time is complete, turn the Instant Pot off and allow the pressure to release naturally for 8-10 minutes before carefully releasing the pressure manually. Once the pressure is released, remove the lid. Transfer the pork tenderloin to a clean plate to rest while you prepare the sauce.