This forum we are using seems pretty good. Is it based on GitHub - silverstripe/silverstripe-forum: Forum module for SilverStripe CMS?
This is a Discourse forum, so it doesn’t run on a Silverstripe installation at all
We’re hoping to archive the old SilverStripe forum module at some stage. It got about half way through a SS4 update from some community devs who needed it for a project, but have since abandoned the work so I assume it’s not used any more =)