Pour water (or broth) into pot. Place brisket on the trivet (fat side up) and lower into Instant Pot. Sprinkle the seasoning packet over the top.
Place the cover on the pot and set timer to 90 minutes on high pressure (meat setting). It will take the IP around 17 minutes to build up pressure before it begins cooking.
When cooking time is done, do a Quick Release. Let the float valve drop and remove the cover (press cancel button). Remove trivet and meat from Instant Pot and place on a cutting board. Cover with foil to keep warm.
Add cabbage wedges, potatoes and carrots to the Instant Pot and place cover on pot. Set timer to 5 minutes on high pressure (pressure cook setting). It will take the IP around 10 minutes to build up pressure before it begins cooking.
When cooking time is done, do a Quick Release. Let the float valve drop and remove the cover.
Place brisket on a serving platter and spoon the vegetables around it. Serve immediately!