When using tkinter on Windows (10) with a >1 HiDpi screen the sizegrip disappear with dpiawareness is on. A minimal example is as follows:

import tkinter as tk
import tkinter.ttk as ttk
from ctypes import windll, pointer, wintypes
windll.shcore.SetProcessDpiAwareness(1)

root = tk.Tk()
btn1 = tk.Button(root, text='btn1').pack(side=tk.LEFT)
sg = ttk.Sizegrip(root).pack(side=tk.LEFT)
btn2 = tk.Button(root, text='btn2').pack(side=tk.LEFT, fill=tk.BOTH, expand=1)
root.mainloop()

Works fine with commented "SetProcessDpiAwareness", but not when using it. This might be related to the tk issues with hidpi and small radio/checkboxes https://bugs.python.org/issue41969

In issue 33656, we determined that tcl/tk *is* dpi aware and that telling Windows so is needed for proper text display.  IDLE now issues the same Windows command (idlelib.pyshell, line 20).  This perhaps should be done by Python itself, but that is not my department.  In any case, without the setting, text in IDLE Windows is much uglier on my 27 inch 2560 x 1440 screen.

IDLE Windows do not currently have sizegrips.  This seems to be standard on Windows. One can resize by grabbing the bottom of the lower right corner. But it is a bit finicky.

When I run your code, I see the small, faint, sizegrip.  Perhaps my screen is not HiDpi enough to see the problem.  In any case, this is a tcl/tk issue.  Perhaps upgrading to 8.6.11 (#43652) will help, as it is supposed to for the radiobutton issue.