User blog comment:MisterWoodhouse/The first specifics on the Unified Community Platform/@comment-31862619-20191016200732/@comment-24006128-20191016201323

The Special:Forum code simply isn't in a place where maintaining it is good for the future of the platform. We have to move on and we've been trying to do so for some time now, so we're finally calling an end to the feature.

If you want to have a forum-style alternative, you can use wiki-style DPLforums when Special:Forum is retired.