The Madden NFL series uses the Frostbite Engine. This engine is developed by DICE, a subsidiary of Electronic Arts (EA). EA has been using Frostbite for the Madden series since Madden NFL 18, which was released in 2017. The Frostbite Engine provides enhanced graphics and more realistic environmental interactions.
The switch to Frostbite allowed the Madden series to improve its visual quality and deliver more immersive gaming experiences. However, the details about the engine's underlying code or specifics about how EA adapted it for Madden are proprietary information not available to the public.
Keep in mind that game development companies sometimes switch engines or update their existing ones, so it's always good to check the most recent sources to confirm this information.