In case it is helpful, here is the error log from a recent full-day IDLE session.

$ python3.9 --version
Python 3.9.0rc1
$ python3.9 -m idlelib.idle
Exception in Tkinter callback
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/tkinter/__init__.py", line 1885, in __call__
    return self.func(*args)
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/idlelib/autocomplete_w.py", line 248, in winconfig_event
    acw_width, acw_height = acw.winfo_width(), acw.winfo_height()
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/tkinter/__init__.py", line 1291, in winfo_width
    self.tk.call('winfo', 'width', self._w))
_tkinter.TclError: bad window path name ".!listedtoplevel4.!frame.text.!toplevel2"
/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/resource_tracker.py:216: UserWarning: resource_tracker: There appear to be 2 leaked semaphore objects to clean up at shutdown
  warnings.warn('resource_tracker: There appear to be %d '
2020-08-20 15:00:38.074 Python[1512:2706287] WARNING: <NSOpenPanel: 0x7ff5a3ed6280> running implicitly; please run panels using NSSavePanel rather than NSApplication.
2020-08-20 16:29:29.880 Python[1512:2706287] WARNING: <NSOpenPanel: 0x7ff5a25566b0> running implicitly; please run panels using NSSavePanel rather than NSApplication.