The Island Sanctuary was announced as a new feature for Endwalker. Specific details are currently sparse, and the only publicly released visual is the concept art shown to the right of this text.
It is planned to be an instanced private island that is relaxing and free from pressures such as having to complete a task each week to remain competitive in raiding, for instance.
According to an interview Yoshi-P conducted with Meoni and Shenpai, the Island Sanctuary will include activities such as raising and tending to crops and animals, build structures, invite and talk to friends, visit their islands, allow minions to roam, etc. However, Yoshi-P has cautioned players not to expect anything on the level of Animal Crossing.