Is this problem still present?

I've used the following script to test:

import tkinter
from tkinter import messagebox

root = tkinter.Tk()
box = messagebox.showinfo("Title", "A Message")

# -- EOF ---

With this script I can close the message box without problems (by clicking on the OK button). Both when running from the command-line and when running from IDLE.

Python 3.9, installer from python.org.