I think the only thing worse than something not being private, is if the fact that it's not private is not common knowledge leading to tons of people thinking it's private.
Lemmy doesn't even show a list of what you the logged in user voted on. But it's trivial to use an external tool to see who voted on what regardless of whose account it is. I think obsecuring information like this does more harm than good, since a lot of people won't actively go out and research what kind of data in their Lemmy account is publicly accessible beyond the data they can see from the website itself.
It's been discussed before that there isn't an easy way to hide who voted for what on a federated platform while still having all the instances correctly count votes for everyone. Therefore, if actually making votes anonymous seems not to be viable, why not just make it public for everyone like Mastodon does? I don't think we should make them inbox items like on Mastodon, or at least not the same inbox as the rest of the notifications so votes don't drown them out. I think a dropdown on the content itself showing who voted on it and in which direction is probably enough. Also a tab on the user page showing a list of everything the user voted on, at least on the logged in user's own page (I mainly want this so I can keep track of what I voted on).
Generally speaking, anyone can correlate the two.
I mean, when a piefed user and a piefed shadow account participate and vote in the same thread, it doesn't take a rocket surgeon to conclude they might be the same person. Look through a handful of the user's comment threads, look for piefed users voting in the preceding comments for confirmation.
Unless the user only votes in threads they do not participate in, and only participates in threads they do not vote in, correlating the two accounts is trivial.