IDLE uses tkinter extensively and runs fine on 3.0 to the upcoming 3.9.  Events remain Events and event.type, event.widget, event.x, and so on continue to work as appropriate for the event type.  As far as I know, the only directly tkinter-related changes were the import names for tkinter and its subpackages.

The same has been true for countless other tkinter users. So until you or someone can produce a short example that only imports tkinter and definitely not anything outside of the stdlib, I (and I think 'we') will assume that the problem is with your code or one of the modules you import or possibly a system-specific bad compilation of tcl/tk/_tkinter.c or mangled tkinter.py.

Some notes to maybe help:
1. When reporting an exception, one should nearly always paste the complete traceback.

2. The first post-import statement in tboplayer.py monkey-patches tkinter with
  tk.CallWrapper = ExceptionCatcher
where ExceptionCatcher must be a class from one of the 3rd party * imports.

To see if one of the 3rd party modules is replacing tk.Event when imported, put 'print(Event)' after 'from tkinter import *'.  You should see "<class 'tkinter.Event'>".  If not, move the import and debug print up.  If so, put debug prints down in your code.

3. Passing non-Events (like False) as the event argument, especially when this unusually possibility is not documented.  A common idiom would be
    def select_track(event=None):
        ...
        if event is not None: ...
A reader should be able to assume that any non-None event is really an event.

Python-list, which I read, would be one good place for any further discussion.