There are two base game bosses you need to defeat in Elden Ring before Shadow of the Erdtree DLC is available. Here’s what you should do before it launches.
https://www.digitaltrends.com/gaming/elden-ring-how-to-start-shadow-of-the-erdtree-dlc/
https://www.digitaltrends.com/gaming/elden-ring-how-to-start-shadow-of-the-erdtree-dlc/