It would be similar to how you do it in Unity. Godot has similar networking to UNET that existed back then. The docs are pretty easy to understand.

Users (and I think Discord too) call the communities servers, and channels are the individual topics/threads in a community. It might not make sense from a hosting perspective but people do call it that

Nah it’s just that they have blocks of the same size. It probably synchronizes terrain using analogous block types where possible, and player position. Basically it has to convert everything into something similar.