I appreciate the additional information, however, a link found in the codeberg link you provided leads to this comment from earnest:

The up arrow is the equivalent of a boost on Mastodon, adding to favorites is represented by a star. The down arrow is equivalent to the Dislike button on Lemmy and Friendica, Mastodon probably doesn't have an equivalent (Dislike will be federated this week). Compared to Lemmy, it works a little differently, as the up arrow there is the equivalent of a favorite.

The comment activity can be checked by expanding the "more" menu and selecting "activity"

This seems to imply that downvotes (reduces) are federated. (And notably, upvotes are now "stars" "boosts" are, uh, "boosts"; this was changed since the linked comment was made)

Or am I totally missing something? That's always and option.