Put the inner pot in the instant pot Base. Push the saute' button setting and set the timer to thirty minutes. Put the butter and let it melt.
Add the onion and the pepper. Let it cook for three minutes, and sprinkle the all-purpose flour. Mix using a ladle until the flour turns creamy. Slowly add a small amount of water to smoothen the roux. This process makes a cream soup.
Pour in the half and half, and add the celery, carrots, and frozen broccoli florets.
Turn off the saute' button setting and cover the pot with the pressure cooker lid. Put the pressure on HI and set the time to two minutes.
When the cooking is done, set your timer to twenty minutes before releasing the pressure.
Cancel the pressure cook button and push the saute' button setting. Add the Velveeta cheese and stir until it's melted. Season with onion and garlic powder. Season with salt and pepper if needed.