Turn on a multi-functional pressure cooker (such as Instant Pot®) and select Saute function. Melt butter in the pot and add garlic. Stir until fragrant, about 30 seconds. Add cauliflower; stir until cauliflower is coated in butter and starting to become tender, about 5 minutes. Add broth. Close and lock the lid. Choose high pressure and set timer for 5 minutes. Allow time for pressure to build.