Hello,
I have noticed that ggplot2 reverses the order of categories when the legend is horizontal (e.g., when legend.position = "top", see repex below). This has been raised as a previous issue (#4715), but I find it quite bothersome in practice (as I frequently need to modify the order of categories in the legend using guide_legend()).

Moreover, I believe that the order of categories in the legend should follow a coherent pattern with the order of categories in the graph, just as it does for vertical legends. This would make more sense.

What do you think about this?
I feel that this should not cause too significant a disruption for ggplot2 users.

# repex : 

iris%>%
  group_by(Species)%>%
  count()%>%
  ggplot(aes(x = n, y = "y", fill = Species))+
  geom_col(position = position_stack())+
  theme(legend.position = "top")