To make these No-Bake Peanut Butter Cup Bars gluten-free, replace the regular graham cracker crumbs with certified gluten-free graham cracker crumbs. Confirm that the powdered sugar, peanut butter, milk chocolate chips, butter, and all packaged ingredients are labeled gluten-free. Some chocolate chips and peanut butter brands may contain gluten-based additives or cross-contact warnings, so check labels carefully. Use clean cookware, measuring tools, spatulas, parchment paper, cutting boards, and storage containers to prevent gluten contamination.