For anyone wondering what this means, my own take is:
Everyone can still read hexbear's content in read-only mode, it is now only the interactions that have been severed, due to too many bad-faith occurrences (many links given in this post, or rather in posts linked to from that post, offered as justification by the various instance admins for why they too defederated from HB) where the HB admins have not upheld their own promises regarding the shared codes of conduct nor their own instructions to their userbase (to constrain the trolling to only inside of communities hosted there, where it is more expected and unfortunately for everyone else even outright encouraged by the admin team).
There are many many instances that still remain federated with HB for those that want that. Especially lemm.ee as the #3 Lemmy instance (after #1 which is Lemmy.World with ~80% of the entire Lemmy userbase, and #2 is lemmynsfw.com), or sh.itjust.works as the #4 instance, but also another USA-based one is lemmy.today - see https://lemmy.today/c/chapotraphouse@hexbear.net. This defederation will help keep Discuss.Online true to its own motto of facilitating friendly discussions without that source of trolling spamming us constantly. Conversely, other USA-based instances that defederate not only from HB but also from lemmy.ml is lemmy.cafe and dubvee.org, and both of those are great options as well (though each quite a bit smaller than DO, and the latter has a significantly more narrow on-ramp to the Fediverse that is more akin to Beehaw that is heavily curated to avoid toxicity - which ofc some people will absolutely love, even as others absolutely will hate:-D).
And before someone mentions midwest.social, there seems to be some controversy surrounding claims of abusive moderation practices on that one. It does have some cool communities such as !theonion@midwest.social and !lotrmemes@midwest.social but you don't need an account on that instance to interact with those.
Anyway it is fantastic to have so many options available! In particular, while the worst excesses of HB are easily avoidable by those of us who are already aware, new users will not know, and many are turned away from the entire concept of the Fediverse to come here and see such, and then leave as a result rather than learn how to block them. i.e., HB having been "opt-out" rather than "opt-in" was hurting us, so I am glad to see that trend reversed. You can always find HB content - nobody has taken that away, though indeed you can no longer interact with it using a DO account, due to the limitations of the tools that we have been provided with.
And this in turn makes the Fediverse friendly - again not so much for us who already knew about HB, but for new users who will not know, yet now have a greater chance of sticking around (rather than be intimidated out) in order to find out how great we are:-).
I am excited to see what will come of this:-).