An island other than the main island of the end is not generated.
Linked issues
Comments

An island other than the main island of the end is not generated.
Since there is no island even if it flew by the teleporter, it is forcibly returned to the main island.
I can not find an island even if I flew from Elytra from the main island.
Sounds like MC-138069.
What other island? Please provide more detail about the issue.