Set Instant Pot to Saute and once it reads Hot, add butter.
Toss in onions, carrots, and celery and cook for 5 minutes, stirring frequently.
Once the onion is translucent, turn off Saute. Add in broccoli and chicken broth. Stir.
Lock Instant Pot lid into place and set seal to sealing. Press Manual and set time to 5 minutes.
Once the timer beeps, release pressure. Remove the lid carefully and select Saute mode.
Stir in milk, cream and garlic. Use a hand immersion blender to break up any chunks of vegetables and puree the soup till smooth.
Turn off Saute. Slowly add cheese while stirring until cheese melts completely.
Taste the soup and add salt or pepper to taste. Serve immediately or let cool and freeze for later.