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.
I’m pretty sure you could request it from any server. Just because it’s federated doesn’t mean the law doesn’t apply to anyone else with personal data.
And it only matters if you care about operating in the jurisdiction of GDPR. Violate it as much as you want if you’re not located there.