To make this Instant Pot Beef & Potato Stew gluten-free, replace the Guinness with a gluten-free stout or omit the beer entirely and substitute it with an equal amount of beef broth or red wine. Ensure that your beef broth and tomato paste are labeled gluten-free, as some commercial brands may contain traces of gluten. The cornstarch thickener is naturally gluten-free, so no additional changes are needed.