Votes are public to not just to the original instance admins though but to any instance admin, right? If you setup your own instance and federate with another, then you should be able to view the votes for any communities on the one you federate with. The only privacy is that the default UI doesn’t display it, but a different UI could:
e.g. the one for this post on kbin.social that shows Lemmy upvotes as favorites.
I feel like this should be more prominently disclosed to Lemmy users.
Another KOReader recommendation here. I typically use it on an eink device but also have it on my phone and it works well.
Looks like for syncing there’s a plugin:
https://github.com/koreader/koreader/wiki/Progress-sync