Combine the 1½ tsp fine grind sea salt, 1 tsp black pepper, and ½ tsp dried crushed rosemary leaves. Mix well and use the seasoning mix to rub all over the brisket.
In the inner pot, combine the beef broth, red wine vinegar, brown sugar and stir.
Slice the mushrooms and add to the pot along with ½ of the bag of cranberries. Slice the onions and add half to the inner pot. Peel and smash the garlic cloves and add half to the inner pot.
Place the reversible rack in the low position and line with the remaining onion slices and sprigs of fresh rosemary if desired. Place the brisket on the rack and top with the remaining garlic cloves.
Put the pressure lid on and set the pressure on high for 60 minutes. Do a full Natural Release, this usually takes about 30 minutes.
Remove the Brisket and place on a cutting board or plate. Pick out the rosemary stems and add any onions that are on the rack into the liquid. Ladle or pour the contents of the inner pot into a large bowl.
Place the brisket back on the rack in the low position with the fat side up and air crisp on 400℉/200℃ for about 10 minutes or until the fat on the brisket is brown and crispy. Remove the brisket and let it rest on a cutting board or plate.
There will be some fat in the inner pot from air crisping, leave that in the pot. Skim off several Tablespoons of fat from the top of the bowl with the juices and add to the inner pot. It's fine if you also add in some juices, but try to get mostly the fat that rises to the top of the bowl of juices. Turn the sear/sauté on high and add half of the flour. Stir to combine. I find sifting the flour in helps to prevent clumps, but it's not totally necessary. Add some more fat from the juices if needed and the remaining flour. Cook, while stirring, for 2 minutes.
Add in the onions, mushroom, garlic, and cranberries from the reserved bowl of juices. Add in just enough of the liquid to get the gravy to the consistency you want. It will thicken some as it simmers. Add in the remaining cranberries and simmer while you slice the brisket. Taste the gravy and add salt & pepper to taste.
Slice the brisket against the grain and place on a serving platter. Pour some of the gravy over the slices. Decorate with fresh rosemary sprigs if desired. Place the remaining gravy into a serving bowl. Serve & Enjoy!