Run your own instance, subscribe to every community, then backup the db.
datahoarder
Who are we?
We are digital librarians. Among us are represented the various reasons to keep data -- legal requirements, competitive requirements, uncertainty of permanence of cloud services, distaste for transmitting your data externally (e.g. government or corporate espionage), cultural and familial archivists, internet collapse preppers, and people who do it themselves so they're sure it's done right. Everyone has their reasons for curating the data they have decided to keep (either forever or For A Damn Long Time). Along the way we have sought out like-minded individuals to exchange strategies, war stories, and cautionary tales of failures.
We are one. We are legion. And we're trying really hard not to forget.
-- 5-4-3-2-1-bang from this thread
As far as I have searched, I didn't find a way to find "every" instance. Most of the popular ones - yes, but far from all.
Also I did not know that each instance copies all pf the data of all other instances into their own db.
But thanks, I will try it out next year.
There's no authoritative list of instances since federation isn't required, but tools like lemmyverse.net will give you a solid list of the ones discoverable from the most well known federations.
My Canadian king 😍