Turn the Instant Pot to saute mode. Add the oil to the Instant Pot. When the oil is hot, saute the onions, garlic, Italian seasoning, cayenne pepper, and pepper for about 30 seconds until they are fragrant.
Add radishes and carrots to the Instant Pot. Saute them for 3-5 minutes.
Next, mix in the celery, yellow squash, cauliflower, and broccoli. Add the broth then close the lid.
Cook on high pressure using the “manual” or “pressure cook” setting for 1 minute. Release the pressure by opening the pressure valve for a few seconds and then closing it. Repeat this motion until all the pressure is released. This will prevent the soup from spraying out the top.
Remove the lid and turn the Instant Pot back to saute mode.
Stir the brown rice flour into the chowder. Continue to mix the soup for 2-3 minutes until the chowder reaches the desired thickness.
Turn off the Instant Pot and allow the vegetables chowder to cool for 10 minutes, then mix in the Greek yogurt and cheddar cheese. before serving.