Board Thread:Support Requests - Designing Your Wiki/@comment-25866598-20161106180139/@comment-27345308-20161106180620

There will be forums no more soon. Special:Forum will be replaced with Discussions and I doubt Staff will enable Special:Forum on request because it will be soon gone from the codebase.

You could read the Discussions FAQ and this blog post for more information.

An alternative is to use wiki-style forums, although they aren't included in the starter pages anymore and the help page for setup is completely broken.