[20Mar2021 04:40:36.204] [Server thread/INFO] [net.minecraft.server.dedicated.DedicatedServer/]: Preparing level "world"
[20Mar2021 04:40:37.229] [Worker-Main-11/INFO] [bettercaves/]: CREATING AND INIT'ING CARVER W DIMENSION minecraft:overworld...
[20Mar2021 04:40:37.232] [Worker-Main-11/INFO] [bettercaves/]: Better Caves config file for dimension minecraft:overworld not found. Using global config...
[20Mar2021 04:40:37.284] [Worker-Main-11/INFO] [bettercaves/]: Using block 'minecraft:lava' as lava in cave generation for dimension minecraft:overworld
[20Mar2021 04:40:37.285] [Worker-Main-11/INFO] [bettercaves/]: Using block 'Block{minecraft:water}[level=0]' as water in cave generation for dimension minecraft:overworld

FWIW, I had Bloxys Structures as one of my mods. Removing it allowed my world to generate and join.

Closing since this is likely due to structure mods you're using calling improper methods during world generation, resulting in server deadlock. The fact that one user fixed the issue by removing a structure mod supports this.

This happens to me, Forge version 36.1.23. Lastest version of BC BetterCaves-Forge-1.16.4-1.1.2.jar

Same

same issue here

If all of you don't mind, please provide more information, like the version of BC you're using, Forge/Fabric version, and a pastebin listing your other mods.