Traitor aims to be a game similar to Among Us. I've never actually played Among Us though, so your mileage may vary. :)
The game provides nodes and mechanics for building and playing 'levels', but has no mapgen, relying entirely on user generated content for the map. A spawn hub should be built at some location, and that location should be set as the lobby spawn point via the "Lobby spawn point" (traitor_lobby_spawn) game setting.
To create a new world/server grant youself free and fly, teleport to your spawn location. and use world edit to create a platform for new players to spawn onto. You may want to build walls around the platform so people can't walk off the edge and fall forever. Some invisible nodes are provided, and nodes that aren't available in creative inventory for server building. You can easily find them by searching the source code for nodes that are not_in_creative_inventory.