% pip3 install tk

#!/usr/bin/env python3

import tkinter as tk

Traceback (most recent call last):
  File "/Users/arghadip/Library/Application Support/CodeRunner/Unsaved/Untitled.py", line 4, in <module>
    import tkinter as tk
  File "/usr/local/Cellar/python@3.9/3.9.5/Frameworks/Python.framework/Versions/3.9/lib/python3.9/tkinter/__init__.py", line 37, in <module>
    import _tkinter # If this fails your Python may not be configured for Tk
ModuleNotFoundError: No module named '_tkinter'

brew install python-tk