Combine beer, ketchup, and cranberry sauce in a medium bowl and set aside.
Set the instant pot on sauté mode “high” and add the olive oil. Salt and pepper the brisket and brown it on both sides - about three minutes per side. Remove brisket.
Turn sauté down to “normal” and add sliced onions to pan. Brown the onions, stirring frequently for about 3-5 minutes.
Place brisket on onions – layering it as needed, then pour beer mixture over brisket. Close the lid and turn it on to “pressure cook” for 60 minutes.
When 60 minutes is up, let it natural pressure release (NPR) for 10 minutes, then let it quick release for about four minutes or until the silver knob goes down.
At this point, the meat should be almost tender. Remove and slice it across the grain (crucial to cut against the grain or it will be tough to chew even if it is cooked properly)
If you are adding carrots and potatoes, add them into the pot, then put the meat back on top of the vegetables. If any of the meat is thinner and seems done, just slice it and don’t put it back in. Put the instant pot on for two minutes of “pressure cook”. When it’s done, let it NPR again for 10 minutes, then quick release and it should be ready to go.
You can now either serve the brisket immediately or let it cool uncovered for about half an hour and refrigerate it to eat up to two days later. You can also freeze the brisket for later use. If I’m not eating it right away, I like to put it in a pan that I can use to heat it back up. I line up the slices of meat, add in the veggies and put some of the juice back in. If there is a lot of extra gravy, store it separately – it’s perfect to put out on the table when you serve the meat.