how do I interact with a community I cannot connect to? Would I need to manipulate the URL in order to "access" it, although this gives the error page not found, of course. (Not the best method of poking another community.)

But that's interesting that it takes some time to sync or whatever. Unfortunately, this immediately creates the illusion that some communities don't exist, and causes people to create a double community. This just happened to me. I created c/whatstheword on my instance...