Votes are not private and never will be.
There have been some discussions about whether Threadiverse software should only federate out the number of votes and perhaps some anonymised voter IDs, rather than information that identifies individual users. This would prevent vote snooping via sites like Lemvotes. However, even if something like that were implemented, instance admins would still be able to snoop on their own users if they so wished. So imo, it’s better to just accept that votes are public information.
Personally I don’t see the issue with it. My principle when it comes to voting is upvoting stuff I want others to see and only downvote things I don’t think anyone would want to see (like spam). So if for some odd reason someone is interested enough to check my voting history, I don’t care. What’s the worst that could happen? Someone on the internet disagrees with my votes? Oh no! How will I ever survive?!
As a side note, Lemmy’s developers seem to have a strong opinion that voter information shouldn’t be displayed publicly. For example, here’s an issue they opened in the Mbin repo. While I disagree with their stance on vote visibility, Nutomic has a valid point there: Lemmy doesn’t mark voting activity as public when federating it out, so there’s an argument to be made that other software should not display individual votes coming from Lemmy.