I'm confused, does this mean that if your account was created on an instance without downvotes you can't downvote thongs elsewhere where they're enabled? How does this work the other way?
Not quite. Their downvotes don't influence our algorithms. So here on Blahaj Lemmy, their downvotes don't do anything even if their instance allows them to down vote.
Basically, our ranking algorithms here don't take downvotes in to account, wherever they come from.
Which means that if you view "hot posts" in a community on our instance and then view the same community on another instance, the ranking of the posts might appear different if they count downvotes.