Pat roast dry. Season liberally with spice mixture.
Set Instant Pot to "SAUTE." Add avocado oil.
Place roast in Instant Pot and brown on all sides. (If roast doesn't fit inside Instant Pot, cut into 2 or 3 pieces and brown in batches.)
Remove roast and place on a large plate or platter. Add onions, beef broth, and bay leaves, stirring to combine. Return roast to Instant Pot and place on top of onion mixture.
Lock lid and close steam valve. Select "MANUAL" and set the cook time for 70 minutes.
When the cook time is over, let the pressure release naturally, which takes approximately 20 minutes. If in a hurry, let the pressure release naturally for 10 minutes and then quick release the remaining steam. Once all steam is released, carefully open lid.
Remove roast and place on a serving platter or large plate. Strain the remaining juices to create a broth. Discard onion and bay leaves.
Return strained broth to Instant Pot, reserving ¼ cup of liquid. Whisk to combine arrowroot powder with the reserved ¼ cup of liquid until no lumps remain. Add mixture to broth, stirring to combine.
Select "SAUTE" and cook broth for 5 minutes or until desired thickness is achieved, stirring constantly. Turn off Instant Pot.