Season chuck roast with salt and pepper. Place roast in the inner pot. Arrange the onions on top of and around the roast.
In a medium bowl, combine celery flakes, garlic powder, broth, and Worcestershire sauce. Pour mixture around the roast. Add bay leaves to the pot.
Close and lock the lid and turn the steam release handle to Sealing. Set your Instant Pot to pressure cook on High for 35 minutes.
When the cooking time is done, press Cancel and let stand, covered, for 10 minutes, then turn the steam release handle to Venting. When the float valve drops down, remove the lid.
Arrange the potatoes and carrots around roast. Close and lock the lid and turn the steam release handle to Sealing. Set your Instant Pot to pressure cook on High for 10 minutes. When the cooking time is done quickly release the pressure.
The roast should be fork-tender. (If more cooking time is needed, continue pressure cooking on High for 5 minutes, then quickly release the pressure.)
Using tongs, transfer roast to a cutting board. Slice roast across the grain and transfer slices to a serving platter.
Using a slotted spoon, remove potatoes and carrots and arrange around the roast.
Skim off fat from cooking liquid and drizzle roast with some of the liquid.