If the community’s server does not track downvotes, then indeed, everyone just sees downvotes by users local to their home instance. Otherwise, downvotes work the same as upvotes - that is, somewhat reliably - unless your frontend or user instance hides them but that’s your problem.
Afaik voting is not federated so you always just see the “local reaction”.
I don’t think so. You see the votes from all federated instances which can still differ
If the community’s server does not track downvotes, then indeed, everyone just sees downvotes by users local to their home instance. Otherwise, downvotes work the same as upvotes - that is, somewhat reliably - unless your frontend or user instance hides them but that’s your problem.