Sauté the Vegetables: Turn the Instant Pot to Sauté (More/High setting) and melt the butter. Add the diced shallots, carrots, red bell pepper, and garlic. Stir and cook for about 5 minutes, or until the vegetables are softened.
Create the Roux: Sprinkle in the flour and stir quickly, ensuring the vegetables are evenly coated.
Add Liquids: Pour in the chicken broth, beer, and liquid smoke. Stir well to remove any flour lumps and scrape the bottom to prevent burning.
Pressure Cook: Secure the lid and set the valve to Sealing. Select Manual (High Pressure) and cook for 5 minutes. Once done, perform a quick release of pressure.
Incorporate Dairy & Cheese: Switch back to Sauté mode and pour in the heavy cream. Whisk until fully combined, then gradually add the shredded Cheddar and cubed Boursin (or cream cheese), stirring continuously until the cheese melts into a smooth consistency.
Season the Soup: Stir in the thyme, Worcestershire sauce, Old Bay seasoning, nutmeg, and hot sauce (if using). Mix well.
Blend for Smoothness: Use an immersion blender to puree the soup directly in the Instant Pot, or carefully blend in batches using a regular blender.
Serve & Garnish: Ladle the soup into bowls and serve with hot pretzels. For extra flavor, sprinkle crumbled blue cheese on top and drizzle with mustard oil if desired.