I run a fairly active forum for old Range Rovers (https://rangerovers.pub), but it just doesn't show up in Google. I don't consider this a problem, since user growth seems to just spread by word-of-mouth - when people get sick of dealing with Facebook pages they start coming to the Forum instead.

It runs on FlaskBB, which is a (reasonably) modern forum written using the Flask web framework.

You'd be amazed how many automated signups it attracts, for something that doesn't even show up on Google.