To make sauce, combine ketchup, barbecue sauce, maple syrup, and half a cup of water. You can also substitute with any BBQ sauce you like (I've also made with Kalbi sauce - 2 cups, no water needed).
To marinate ribs, rub onions, garlic, salt and pepper onto both sides of ribs. Marinate overnight for best results.
Open Instant Pot. Roll up ribs and place into instant pot vertically.
Add sauce and 1/2 cup of water.
Close Instant Pot. Select meat or manual, high pressure cooking, for 25 minutes.
When done, do a Quick Release and remove ribs. You can also wait for pressure to release naturally if you want.
Thicken sauce by selecting Saute. Make a cornstarch slurry by combining 2 tablespoons of cornstarch with 1/2 cup cold water. Pour slurry into sauce. When this bubbles, it is done.
Pour sauce over ribs and serve. Or you can place into oven to caramelize the top. Set your oven to broil at 400F for about 10 to 15 minutes.