I think it's local and depends on the server. I can't see Lemmy downvotes from Kbin, but I can see Kbin's downvotes on Lemmy posts. I'm still trying to wrap my head around it myself.
I think I remember reading some instances just turn off downvoting entirely.
I have Jerboa on /e/ OS and I can't downvote. But I'm on the reddthat instance (not sure why) so maybe that plays a role too?
OK its more complicated. I can downvote when I view replies in my inbox. But I cant downvote when I view replies in my profile of when browsing posts in channels.
You can, but I don't think downvotes get federated to other instances. So even if you downvote on Jerboa, I can't see it on Kbin. Something about how the Activitypub protocol works.
Assuming it’s your downvote, I can see one on their post via Memmy. https://i.imgur.com/qRdoY97.png
My Administrator said "As everything else is federated, it would be strange if downvotes are not"
Yep, that'd be your local squad doing that. All you'll ever get from me is upvotes or nothing.