Slice onions and garlic and place in bottom of the pressure cooker.
Season beef and sear in olive oil, then place on top of the onions.
Whisk the sauce and pour over the beef.
Close the Instant Pot and set for 75 minutes on manual.
Open the steam valve and release the pressure before attempting to open the cooker.
Remove beef; strain onion and garlic from the sauce and discard.
Refrigerate beef overnight and slice thinly across the grain for best (and easiest) slicing results.
Skim fat from pan sauce and reduce by half in a saucepan if you want to use it on the beef, refrigerating overnight and removing the fat that rises and solidifies at the top.