Preheat the Instant Pot to the "Saute" option.
Season short ribs with kosher salt and pepper.
Place them in one layer in the pot and let them sear (~7-8 minutes).
As the meat sears, chop the onions and carrots. After 7-8 minutes have passed, flip to the other side and let sear for ~4-5 minutes.
Once meat is nicely browned, transfer to a plate and decreasee heat to medium.
If your pot has >1 tbsp oil accumulated from the meat, pour it out. Otherwise, add onion, carrots, garlic, spices/herbs and let it cook, stirring occasionally, for 5-6 minutes until softened. Season with salt + pepper, to taste.
Add stout and place the short ribs back into the pot.
Seal the Instant Pot, ensuring that the venting switch is set to the "Sealing" position. Then press the "Stew" option and set manual time to 35 minutes on high pressure.
When the timer beeps, allow it to go into "Keep Warm" setting for 15 minutes, then switch the venting tab to the "Venting" position and when the steam has been released, carefully remove the lid of the pot.
Remove the meat and veggies and transfer to a plate.
Try to skim most of the fat from the sauce off with a spoon.** Add balsamic vinegar and turn it back to the "Saute" option. Allow it to boil until it reaches a glaze-like consistency. Pour the glaze over the short ribs and serve!