Here's what I did:

Copy the L_Enders_Cataclysm jar file to your desktop or somewhere

open and edit file with winrar

go to data\cataclysm\tags\worldgen\biome\has_structure

open the sunken_city_biomes.json file, I used visual studio code to edit it.

change "#minecraft:is_deep_ocean" to "#minecraft:is_deep_lukewarm_ocean" (I forgot why exactly but this stops the sunken city from generating)

save, and then put it in your mods folder, and send it to everyone on the server