I found !ttrpg.network (not sure how to link from kbin, but that’s what i search for) and it seems to have a lot of good, active communities. Other than that, I haven’t found anything more populated.
@EmpeRohr Off the Fediverse, dndbeyond.com and 5esrd.com are actually more than sufficient to get someone started. I do recommend trying to get either the starter or essential’s kit because you’ll also get the digital version on dndbeyond.
If it was already tried with this specific cable and it didn’t work, then this cable doesn’t have the capability built in. Some cables like this have a bridge in the cable that allows pc to pc communication.