Add the chicken stock and apple cider vinegar to the Instant Pot insert, followed by the chicken thighs.
Sprinkle the garlic powder, paprika, and salt on top of the chicken.
Finally, pour ¾ cup of the BBQ sauce over the chicken thighs. Do not stir.
Attach the lid and ensure the valve is in the “sealing position”.
Set for manual high pressure for 15 minutes.
When the timer finishes, allow the pressure to naturally release for 10 minutes. Then, quickly release any remaining pressure by switching the valve to the “venting” position.
Transfer the chicken to a bowl and shred it by pulling it with 2 forks.
(Optional) If you like a thick sauce on your sandwich, turn the Instant Pot to the "Saute-Normal" function and whisk in 2 tbsp of flour. Cook, stirring occasionally, for 2-3 minutes or until the sauce has thickened enough to coat the back of a spoon.
Return the chicken to the pot and add the remaining ¼ cup of BBQ sauce.
Serve immediately.
Store any leftover BBQ chicken in an airtight container in the fridge for up to three days.