"In a press release, EA confirmed that to receive the free upgrade of Madden 21, you'll need to purchase the game on Xbox One by December 31, 2020 and upgrade to the Series X by March 31, 2021."https://www.gamespot.com/articles/madden-nfl-21-confirmed-for-xbox-series-x/1100-6476974/

You have to purchase the game before a certain date and upgrade to next gen before. a certain date to get the free update.