PieFed.zip takes an interesting approach: it blocks the most controversial instances but not as defederations i.e. at the instance level, and instead does so automatically for every new account upon sign-up, then sends the user a message explaining how to remove that block. From there they can unblock, reblock, back and forth as they choose at will. It thus makes federation with hexbear and Lemmygrad as opt-in rather than opt-out or obligatory or neglected as all other instances across the Threadiverse do.

I do not recall if it does this for lemmy.ml as well - I would suspect not, sadly, but then again it would be fairly unique in that respect if it did, as virtually no major instances do so.

And as far as far-right instances, those do not really exist, though nonetheless the historical ones are in the defederation list (exploding heads, freespeechextremists, and ofc threads.net:-P), and surely over time new instances could be added as well.

Finally I will add that I've never seen the tiniest hint of documentation for any of this - not in https://piefed.zip/defed_policy, or the welcome messages in their !announcements@piefed.zip or !home@piefed.zip local communities, and now I don't see their listing anywhere in the instance picker site, despite trying multiple host instances of that including themselves. I only know about this since I too questioned how Newbie-friendly any instance was that federates with the above-mentioned pair, and the instance admin told me about this, but even now months later I still don't see an official description written down about this somewhere easily accessible by people.

The Threadiverse is still very much a Work-In-Progress! But... it's getting better, and PieFed.zip is a major part of that progress, it looks to me.