Removing the call "self.grab_set" in configdialog.py (line 87 or so) and help_about.py (line 47 or so) appears to fix the problem with the main window freezing when the modal dialog is destroyed on macOS. "Grab" has never worked properly on Tk on the Mac, but it has additional problems in the Cocoa implementation of Tk; it causes all kinds of problems with the event loop and is best avoided altogether. If the call to grab is crucial on other platforms, it can be wrapped in a call to "tk windowingsystem ne aqua" to exclude the Mac. If other modal dialogs present similar behavior on the Mac, look for calls to grab and try omitting that call. I'll leave it to someone else to propose a thorough patch, but this should point you in the right direction.