只需将group = clarity放入stat_summary的aes中。您还需要添加position_dodge：

ggplot(diamonds |>  filter(cut=="Fair"), 
       aes(x=cut, y=price, color=clarity )) + 
  scale_color_brewer(palette = "Dark2", guide = "none")+ 
  geom_violin(fill = "gray80", linewidth = 1, alpha = .5) +
  geom_sina(alpha = .25) +
  coord_flip()+
  stat_summary(fun.data = "mean_se", colour = "black", 
               linewidth = 1, size = 0.5, aes(group = clarity),
               position = position_dodge(0.9))

问题是你把x轴设置为cut，当你真的希望它由clarity来设置的时候。对于小提琴图，它会错开它们来显示点，但是stat_summary不起作用。如果你设置了x=clarity，那么所有的图元素都会被x-axis组正确地设置：

library(ggplot2)
library(ggforce)
ggplot(diamonds |> dplyr::filter(cut=="Fair"), aes(x=clarity, y=price, color=clarity )) + 
    scale_color_brewer(palette = "Dark2", guide = "none")+ 
    geom_violin(fill = "gray80", linewidth = 1, alpha = .5) +
    geom_sina(alpha = .25) +
    coord_flip()+
    stat_summary(fun.data = "mean_se", color = 'black', linewidth = 1, size = 0.5, )