Trim and cut the chicken into 1-inch pieces; season with black pepper.
Whisk soy sauce, bourbon, brown sugar, ketchup, broth, vinegar, garlic, ginger, red pepper flakes, and sesame oil in a bowl.
Set Instant Pot to Sauté. Add oil and cook onion until softened, about 3 to 4 minutes.
Add chicken and stir for 2 minutes to lightly sear the edges.
Pour in the sauce and scrape up any browned bits from the bottom.
Cancel Sauté. Lock the lid and cook on High Pressure for 7 minutes.
Let pressure release naturally for 5 minutes, then quick-release the rest.
Stir cornstarch with water to make a smooth slurry.
Turn Sauté back on. Stir in the slurry and simmer, stirring, until the sauce is glossy and thick, 1 to 3 minutes.
Serve over rice and garnish with green onions and sesame seeds.