TL;DR (libera.chat version): In May 2021 Andrew Lee (legal owner of freenode.net) started to take over Freenode. Not liking that, unsure of the future, Freenode Staff resigned and moved to libera.chat.
TL;DR (freenode.net version): In April 2021 Tom Wesley (Head of Freenode Staff - a group of volunteers managing freenode services) tried to take over Freenode DNS. Andrew Lee disagreed. They went to lawyers. Tom lost. So Freenode Staff moved to libera.chat and set up everyone against Andrew, thus destroying Freenode. Andrew took over of what's left.