Set Instant Pot to 'sauté' setting. Once the pot is hot, add the ground beef and ground chuck. Brown and crumble beef until no longer pink. Drain and remove to a separate plate and set aside.
Wipe pot, if needed. With the setting still on 'sauté,' add the onion and green pepper and cook until softened, about 4-5 minutes.
Add the ground beef back to the Instant Pot, along with vinegar, sugar, mustard, bbq sauce, ketchup, garlic powder, salt, pepper, and water. Scrape the bottom of the pot to remove any browned bits (to prevent a BURN warning) and stir thoroughly to combine.
Cover, place the lid into lock position and make sure the valve is in the 'sealing' position. Press the manual button and cook on high pressure for 6 minutes. **Remember that it will take the IP about 15 minutes to come to pressure and then will count down from 6 minutes**
When timer goes off, do a quick release by turning the valve to the venting position and letting steam release until the pin drops. (I like to place a folded kitchen towel over the valve so that it catches the steam.) Mixture will thicken as it sits, so if it seems too watery, let sit for 5 minutes before serving.