I've been searching for this functionality on kbin as well, but I don't think it's implemented yet. JustinFTL's recommendation to boost stuff is not private, while usually the saved items are.
Upvoting isn't private either, you can scroll to the bottom of any post on kbin and see a list of everyone who has "favourited" a post. All of your own also get collected to https://kbin.social/fav
Serverside not the way it's implemented I'd imagine, no, but there is no need to have it displayed so prominently on the UI for the users - it isn't on Lemmy for example.
Though it's more understandable if you think of the implemention more like Twitter/Mastodon likes rather than Reddit upvotes, but as a Reddit refugee, it just feels weird to me personally.