Set the Instant Pot to Saute mode. Add the avocado oil and diced onion, and cook for about 2 minutes until softened.
Add the minced garlic and cook for about 30 seconds, until fragrant.
Pour in the chicken stock, then add the chopped chicken and broccoli florets.
Secure the lid, ensure the sealing valve is closed, and set the Instant Pot to Soup mode for 6 minutes.
When the cooking time is complete, manually release the pressure.
Stir in 1/2 cup of the shredded cheddar cheese until fully melted and combined.
Stir in the heavy cream and season with salt and pepper to taste.
Serve warm and top with additional shredded cheese if desired.