Hi @cmues,
If I understand correctly, you need horizontal customized boxplots.
This should get you pretty close:
library(tidyverse)
df <- data.frame(b0 = rnorm(50),
b1 = rnorm(50, 1),
b2 = rnorm(50, 0.75, 0.3),
b3 = rnorm(50, 2.75, .25))
df_long <- pivot_longer(df, cols=1:4)
observed <- data.frame(b0 = 0.15, b1 = 0.79, b2 = 0.76, b3 = 2.71)
observed_long <- pivot_longer(observed, cols=1:4)
# Get the calculated 'boxplot' statistics
b1 <- boxplot(value ~ name, data=df_long, stats=keep)

keep <- as.data.frame(b1$stats)
names(keep) <- names(df)
keep$position <- c("lower_whisker", "lower_hinge", "median",
"upper_hinge", "upper_whisker")
keep_long <- pivot_longer(keep, cols=1:4)
keep_wide <- pivot_wider(keep_long, names_from=position, values_from=value)
ggplot(data=keep_wide) +
geom_segment(aes(y=name, yend=name, x=lower_whisker, xend=upper_whisker),
colour="grey80", size=2) +
geom_segment(aes(y=name, yend=name, x=lower_hinge, xend=upper_hinge),
colour="blue", size=5) +
geom_point(data=observed_long, aes(y=name, x=value), col="red", size=2) +
labs(x="Value", y="Coefficient") +
theme_bw()

Created on 2021-02-13 by the reprex package (v1.0.0)
HTH