This is a simple datapack/mod that removes Terralith's introduction message when creating a world.
Modpack devs are free to use this if they so desire; just stick it in your modpack and it should effectively prevent Terralith from making any chat messages on first world load. This is especially useful for modpack devs that don't want a ton of chat spam on first load, or don't want users confusingly joining the wrong Discord server.