Hi @perlatex,
They are just strings so you can do some simple manipulation to get them into format suitable for plotting:
suppressPackageStartupMessages(library(tidyverse))
# Can use the 4 digit code
ggplot(iris, aes(Sepal.Width, Sepal.Length)) +
geom_point() +
labs(title = "I want to use \U0284 ")

# So, how to convert?
old_strings <- c("<U+0282>","<U+0283>","<U+2C71>")
tmp <- gsub("[<>+]", "", old_strings)
tmp2 <- gsub("U", "0x", tmp) # This prefix means 'interpret as base 16'
new_strings <- intToUtf8(tmp2, multiple=TRUE)
ggplot(iris, aes(Sepal.Width, Sepal.Length)) +
geom_point() +
labs(title = paste0("I want to use: ", new_strings[1]),
subtitle = paste0("And these: ", new_strings[2]," ", new_strings[3]))

Created on 2022-02-25 by the reprex package (v2.0.1)