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.