Set Instant Pot to saute. Add the ground beef, garlic and onion and cook until meat is no longer pink. Drain, if needed.
Add the ketchup, mustard, brown sugar, Worcestershire sauce, water, salt, pepper and cayenne pepper to the pot. Mix well.
Place the cover on the pot and set timer to 5 minutes on high pressure (pressure cook setting). It will take the IP around 9 minutes to build up pressure before it begins cooking.
When cooking is done, let it release naturally for 10 minute. Then do a quick release. Remove cover, stir and let sit for 10 minutes before spooning into buns and serving. Top with pickle slices, if desired.