If they didn't has discord/slack/reddit, it's not worth joining.
Someone really enthusiastically started a forum, added 420 different sub-areas and sub-forums. All of which have a maximum of 1-10 posts. Most of them by the forum admin.
Different folks, different strokes I guess.
If I see a “community” require Slack or Discord, it instantly gives me bad vibes, and I’m almost guaranteed not to join or visit.