I guess I’m not the only one that happens to this, I follow communities with the same theme in different instances, it’s not unusual then to see the same link sent by the same person in both, not a crosspost, the same link sent separately. ¿Is there any, let’s say, correct protocol on how to interact with this? You know, do I vote for both? One positive and the other I ignore? What if I want to comment? Do I make the same comment on both?
I think that this reflects “real life”.
You can go to a pub, spout some nonsense and cross the road and spout it again. Each time you are likely to have a different audience, but there’s no guarantee that someone else crossed the road with you.
In the fediverse the same is true. Each community is distinct, even if they’re called the same thing and have shared participation.
You can choose to participate in whichever one you want to, or all of them. There’s no karma associated with voting, it’s about visibility in that community.
If you think it warrants a vote or comment, then do. If you don’t, then don’t.
There’s no right answer here. Do what you think will improve the community you are part of.