Something like that??? (if i understood your question!!!)

summary_data <- data %>%
  group_by(x1) %>%
  summarize(
    mean_y = mean(y),
    sd_y = sd(y)
  )

ggplot(summary_data, aes(x = x1, y = mean_y)) +
  geom_bar(stat = "identity", fill = "#336699") +
  geom_label(aes(label = round(mean_y, digits = 2)), position = position_nudge(x=-0.2, y = -0.5)) +
  geom_errorbar(aes(ymin = mean_y - sd_y, ymax = mean_y + sd_y),
                width = 0.2, 
                size = 0.8,  
                color = "darkred") +
  xlab("x1") +
  ylab("y") +
  theme_classic(base_size = 12) +
  coord_cartesian(ylim = c(0, max(summary_data$mean_y + summary_data$sd_y) * 1.1))