Using the sauté setting on a 6-quart Instant Pot, add a bit of the vegetable oil to the pot. When the oil is sizzling, add the seasoned chops, browning them on each side, working in two batches. Remove the browned chops to a plate and reserve. Add additional oil if needed to complete the browning process.
Add the mushrooms, onions, dry onion soup mix, and vinegar to the drippings in the IP, cooking for a minute or so. Add the broth, then place the browned chops on top.
Lock the IP lid into place. Using the manual button, choose the High-Pressure setting for 8 - 10 minutes, bringing the IP to full pressure. When the timer sounds, use a natural release for 15-20 minutes. Unlock and remove the IP lid, removing the cooked chops to a plate.
Whisk the prepared cornstarch slurry into the liquids that remain in the IP. Using the sauté setting once again to bring the sauce to a simmer. Cook the sauce just until nicely thickened, 1-2 minutes, stirring often.
Serve the pork chops smothered with the prepared mushroom and onion gravy at once.