An instance simply receives updates from all the communities to which at least one user on the instance has subscribed.
Instances do not send updates to every other instance on the fediverse, only the ones where there are users that follow the content in question.
That still means the differences will be small, as every reasonably sized instance is going to have at least one subscriber to every reasonably sized community.
Except I think your instance affects what you see. Not all communities and instances are replicated everywhere.
That’s not an algorithm.
An instance simply receives updates from all the communities to which at least one user on the instance has subscribed.
Instances do not send updates to every other instance on the fediverse, only the ones where there are users that follow the content in question.
That still means the differences will be small, as every reasonably sized instance is going to have at least one subscriber to every reasonably sized community.