MC-214865 has reported this bug, that issue has been resolved as "Fixed" in 21w15a, but actually this bug was not fixed, there will still be extreme terrain in 21w15a and 21w16a. Even if the world-gen had back to 21w05b, but the world-gen of Floating islands world type still looks like AMPLIFIED world, just like 21w06a to 21w14a. This bug is exist since 21w06a, but it's not exist in 21w05b or earlier version.