Edit: obligatory explanation (thanks mods for squaring me away)…
What you see via the UI isn’t “all that exists”. Unlike Reddit, where everything is a black box, there are a lot more eyeballs who can see “under the hood”. Any instance admin, proper or rogue, gets a ton of information that users won’t normally see. The attached example demonstrates that while users will only see upvote/downvote tallies, admins can see who actually performed those actions.
Edit: To clarify, not just YOUR instance admin gets this info. This is ANY instance admin across the Fediverse.
Just the other day, the computers of Kolektiva.social (mastodon instance) got seized by the FBI.
Well, it wasn’t the other day - it was back in May. It was the other day that its users were notified that it happened.
https://kolektiva.social/@admin/110637031574056150
I wouldn’t make any assumptions about the security of a particular instance of Lemmy or the locations of backups of the database that a developer or admin may have for testing.