Rinse pork, cut into large chunks and sprinkle with black pepper.
Slice onion, mince garlic and set aside.
Add oil to Instant Pot and choose the “saute” option.
Once the oil is hot, add meat to Instant Pot and sear, working in batches, then remove. Saute onion and garlic, scraping the bottom of the pot.
Mix the remaining ingredients in a separate measuring cup. Pour in the Instant Pot and deglaze.
Return the meat to the pot, along with the onion and garlic.
Place the cover on the Instant Pot and set the vent to “seal.” Click the “Pressure Cook” button, and adjust the time to 20 minutes.
Allow to rest for 10 additional minutes, then carefully adjust the vent to release the remaining pressure.
To thicken the sauce further, choose “saute” and cook until the sauce is to your liking.
Serve the pork adobo over white rice, along with some chopped scallions.