It is possible to add min-max values as follow:

library(tidyverse)

# Demo data
df2 <- Orange

# Compute summary statistics
# Create labels to be added at the end of the lines
data_ends <- df2 %>%
  group_by(Tree) %>%
  summarise(
    min_val = min(circumference),
    max_val = max(circumference)
  ) %>%
  mutate(label = paste0("[", min_val, " - ", max_val, "]"))
#> `summarise()` ungrouping output (override with `.groups` argument)


# Add min-max values
ggplot(df2, aes(x = age, y = circumference)) +
  geom_line(aes(color = Tree)) +
  scale_y_continuous(sec.axis = sec_axis(~., breaks = data_ends$max_val, labels = data_ends$label))

Question:
how to add BOTH the min and also the MAX values
at the end of each line?.

Thanks/Merci!