It is the first and last DLC. We have no plans to add more content to Elden Ring. [...] FromSoftware's style of doing things is that it generally does not allow the future of an IP to be easily locked, so it is better to leave some possibilities. But as far as "Shadow of the Erdtree" is concerned, it is the only DLC.
[...]
Elden Ring emphasizes the exploration and adventure of the big world. In order to provide such an experience, a vast and huge scene is inevitably needed. Therefore, instead of splitting it into several parts, it is better to simply make one big. If they were sold separately, the freedom of exploration and sense of adventure would be reduced.