If using frozen chicken, separate pieces so they are not stuck together before adding to the Instant Pot.
Place the chicken breasts in the Instant Pot; it's fine if they overlap.
Pour in 1 1/2 cups of chicken broth (or water or pineapple juice). Sprinkle salt, pepper, onion powder, Italian seasoning, paprika, red pepper flakes (if using), and minced garlic over the chicken. Place the butter on top, if using.
Secure the lid and set the valve to sealing. Select Manual/Pressure Cook: 15 minutes for fresh/thawed breasts or 25 minutes for frozen breasts. The pot will take about 10 minutes to come to pressure.
When the cook time ends, allow a 10–15 minute natural pressure release, then carefully open the valve to release any remaining pressure.
Check the internal temperature; it should reach at least 165°F (74°C). If done, transfer the chicken to a large bowl and shred with forks or chop as desired.
Return some cooking liquid to the shredded chicken as needed to keep it moist and flavorful, then serve or store.