On a Mac, python tk mainwindows do not automatically grab focus or come to the surface. They are often hidden under other Windows. You need to click on the Python launcher icon that gets added to the end of the Dock to force that window to the front and make it take focus.
There is a workaround in Python to force the main window to the front and grab focus.
See my FolderIn or FolderOut or ePub3-itizer plugin code that uses this workaround for tk graphics to work as expected on a Mac
See the needed code here:
https://github.com/kevinhendricks/eP.../src/plugin.py
the bulk of the Tk stuff starts near line 262. The added code is under the darwin if.