If you downvote my comments they do not register on my instance. It is more than the lack of a visible button, the downvotes do not federate.
Edit: to be clear, this post is on lemmy.world, so I can be downvoted here (even though I won’t see it unless I browse from lemmy.world). And from lemmy.world you can appear to downvote things on instances without downvotes, but you are basically just downvoting the local copy of the thing. The downvote never gets sent through, it just lives on your instance.