In March 2021, McDonald's responded to requests for gluten-free buns saying they "have no plans" to offer them: https://www.mcdonalds.com/us/en-us/faq/can-you-offer-gluten-free-buns.html

Millions of people around the world are either celiac or have adopted a gluten-free lifestyle. By offering (or even piloting) specifically gluten-free items, McDonald's can cater to and win the loyalty of this growing market segment while demonstrating leadership in the industry.