Like the title says, if you want to upvote something on KBin, you should use the Boost link, not the upvote button (Why? Don’t know…)
The upvote button doesn’t seem to do much, but Boost accomplishes what Reddit’s upvote did. So if you’re looking to encourage a post, use the Boost link.
Upvotes and downvotes do get synced across instances. There are some issues with how that works atm, basically, sometimes ur vote will only count on the instance you are on, but that’s not actually how it’s supposed to work.