You probably came to this article because you expected caves and cliffs in the new Minecraft 1.17 "Caves & Cliffs" update. This is not a bug in your server, Aternos or the server software: There are no new caves or cliffs in Minecraft 1.17.
Mojang has decided to split the new update into two parts, and the now released version 1.17 only contains part of the promised "Caves & Cliffs" update. Most notably, it doesn't contain new caves or cliffs. The missing features will probably be added in 1.18 at the end of 2021. You can read more about why Mojang made that decision and what you can expect in the official announcement here: https://www.minecraft.net/de-de/article/a-caves---cliffs-announcement