according to https://nlnet.nl/project/Flarum, @nlnet funded #Flarum to implement #ActivityPub in 2023 for release in Flarum 2.0 which is now in beta but I can't find any reference to it being included in the beta but I see @luceos responded to someone what its still under development quite recently.
https://mastodon.social/@luceos@fosstodon.org/113560228111805921
@liaizon@social.wake.st fosstodon seems to be down at the moment, but I don't believe Flarum has started their ActivityPub work, or if they have, it is not at a level for demo yet.
I can't say whether the NLNet project was ever completed.
@liaizon @nlnet we have made some initial steps integrating federation into flarum, but it was never part of our scope for 2.0. Due to personal circumstances we decided to postpone our efforts for federation entirely and notified @nlnet of this decision not too long ago. Flarum won't have this capability for the foreseeable future.