Turn on a multi-functional pressure cooker (such as Instant Pot®) and select Saute function and allow pot to heat. Add butter and melt. Add sausage and chopped onion. Stir until sausage is crumbled and onions are browned, about 5 minutes. Stir in pumpkin and 1 cup of chicken broth. Add remaining 2 cups chicken broth, 1 cup at a time, stirring well after each addition. Close and lock the lid. Cancel Saute function.

Select Soup setting according to manufacturer's instructions; set timer for 10 minutes. Allow 10 to 15 minutes for pressure to build.

Release pressure carefully using the quick-release method according to manufacturer's instructions, about 5 minutes. Unlock and remove the lid. Stir in cream, salt, sage, and garlic. Serve immediately.