It looks like the IRC link on forum.dlang.org pages, under the "Community" tab of the header, still links to irc://irc.freenode.net/d even though that channel is long gone and the IRC link on dlang.org pages has linked to irc://irc.libera.chat/d for a while.
I think it should link to irc://irc.libera.chat/d instead.
Updating the web/static/dlang.org submodule should fix this.
From https://forum.dlang.org/post/ynxtbriectexgfuhtsbk@forum.dlang.org:
Updating the
web/static/dlang.orgsubmodule should fix this.