Make the BBQ Sauce:

Heat 1 tablespoon olive oil in a small saucepan, add the minced onion and saute 4-5 minutes until the onion begins to soften. Stir in garlic and cook 30 seconds. Add cider vinegar through salt.. Bring to a simmer, then stir in ketchup. Cook over low heat 15 minutes, until thickened.

To make immediately: 

1. Place the pork loin in the Instant Pot and pour in the BBQ sauce. Cover, seal, and cook on high pressure for 45 minutes. Let the pressure naturally release, then open the Instant Pot and check the temperature of the pork with a meat thermometer.
2. Remove the pork from the Instant Pot and shred. Return the shredded pork to the Instant Pot and stir to coat the meat with the BBQ sauce.
3. Serve.

To cook from frozen: 

1. Dump the frozen pork and sauce in Instant Pot. Add 1/4 C of water to the bag and shake to get any remaining BBQ sauce from the bag. Pour the water/sauce mixture into the Instant Pot. Cover, seal, and cook on high pressure for 60 minutes. Let the pressure naturally release, then open the Instant Pot and check the temperature of the pork with a meat thermometer.
2. Remove the pork from the Instant Pot and shred. Return the shredded pork to the Instant Pot and stir to coat the meat with the BBQ sauce.
3. Serve.