Jo0001

1.16 & older on 1.18+ servers

[00:00:00 WARN]: [ViaBackwards] Custom worlds heights are NOT SUPPORTED for 1.16 players and older and may lead to errors! [00:00:00 WARN]: [ViaBackwards] You have min/max set to -64/384

Those messages sound familar to you?

Then you have 3 options:

1. Only allow 1.17.x players
2. Use 1.17 as server version (instead of 1.18)
3. Use a datapack (thats why you're probably here)