Trim and cut the chicken thighs into 1–2-inch pieces and set aside.
In the Instant Pot, add chicken, soy sauce, sesame oil, minced garlic, grated ginger, rice vinegar, red pepper flakes, brown sugar, chicken broth, and 1/4 cup water; stir well to combine.
Close the lid and seal the pressure valve. Cook on High Pressure for 5 minutes.
Allow a 10-minute natural release, then carefully release any remaining pressure and open the lid.
Select Sauté on Low to bring the sauce to a simmer.
In a small bowl, whisk 2 tablespoons cornstarch with 2 tablespoons water until smooth to make a slurry.
Stir the cornstarch slurry into the Instant Pot and cook on Sauté, stirring gently, until the sauce thickens, about 3–5 minutes.
If a thicker sauce is desired, mix an additional 1 tablespoon cornstarch with 1 tablespoon water or juice and add to the pot, cooking briefly until thickened.
Turn off the Instant Pot and let the chicken rest for 5–7 minutes to allow the sauce to set.
Serve the chicken over rice and garnish with sliced green onions and sesame seeds.