In a shallow dish, combine the flour with a few shakes of salt and pepper. Dredge the chicken thighs in the flour mixture.
Turn on the saute function in the Instant Pot. Drizzle in some olive oil and saute the chicken thighs on both sides until the outsides are no longer pink. Remove to a plate.
Add the bell pepper, onion, garlic, white wine, broth, capers, herbs and tomatoes to the pot (keep it on the saute function just for a minute or two and use the liquid to deglaze/scrape up the chicken bits from the bottom of the inner pot). Turn to "off."
Return the chicken thighs to the pot and add the chicken breasts.
Close the lid and manually set to 10 minutes on high pressure. (Make sure steam valve is in the "sealed" position).
When the timer goes off, release the steam valve, using proper precautions.
Open the lid and stir.
Add 1 teaspoon salt (or to taste).
Let sit for a few minutes to allow the sauce to thicken. If you want to thicken it further, you can set to saute again.
Notes
If you want the sauce to be thicker, drain some of the liquid out of the tomatoes before adding to the pot.