On Windows 10: when I start 3.7.8 IDLE in Command Prompt with
  C:\Users\Terry>py -3.7 -m idlelib
and try Open Module with 'os.path', I get this traceback in Command Prompt.

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Programs\Python37\lib\tkinter\__init__.py", line 1705, in __call__
    return self.func(*args)
  File "C:\Programs\Python37\lib\idlelib\query.py", line 148, in ok
    entry = self.entry_ok()
  File "C:\Programs\Python37\lib\idlelib\query.py", line 218, in entry_ok
    file_path = spec.loader.get_filename(name)
  File "<frozen importlib._bootstrap_external>", line 406, in _check_name_wrapper
ImportError: loader for ntpath cannot handle os.path


The same action displays ntpath.py in 3.8.5 and  3.9.0b5.  Line 219 in query.py is the same as 3.7 query.py line 218 above.  I conclude that the problem was a bug in importlib that was fixed more recently than your version of 3.8.  Hence closing.