Really grateful that a project like this took on the task to ask for legal advice, and extra kudos for actually releasing a statement based on their understanding of the legal advice. Hopefully will be useful to lots of similar organizations.
Libera.chat seems to say that even if Ofcom thinks they have a case, they don't as Libera's user base doesn't have enough UK users:
> The exact fraction of the UK’s online population that must use a given service to be considered “significant” is unknown, but based on our counsel’s observations of Ofcom’s previous regulatory actions, it appears to be much higher than our internal estimates of how large our UK user base is.
Libera.chat seems to say that even if Ofcom thinks they have a case, they don't as Libera's user base doesn't have enough UK users:
> The exact fraction of the UK’s online population that must use a given service to be considered “significant” is unknown, but based on our counsel’s observations of Ofcom’s previous regulatory actions, it appears to be much higher than our internal estimates of how large our UK user base is.
Related submission with 788 comments from ~1 week ago: "4Chan Lawyer publishes Ofcom correspondence" - https://news.ycombinator.com/item?id=45614148