I don't know anything about appJar (looks interesting!) but any issue like this is almost certainly a Tk issue, since Python's tkinter provides a fairly lightweight wrapper around calls to Tk.

As far as I can tell from a quick test, it appears that the difference here is due to some change in the macOS Cocoa Tk behavior in more recent versions.  As documented, the python.org 3.6.5 macOS 64-bit-only Python uses its own Tcl/Tk 8.6.8 while the 64-bit/32-bit installer continues to link with an external Tcl/Tk 8.5.x version. For that variant, the system looks first in /Library/Frameworks for third-party Tcl and Tk 8.5.x frameworks, such as the recommended ActiveTcl version (https://www.python.org/download/mac/tcltk/) and, if none found there, falls back to the Apple-supplied Tcl/Tk 8.5 frameworks in /System/Library/Frameworks.  With the recommended ActiveState 8.5.18 Tcl/Tk version installed, the tooltips also do not appear just like with the 64-bit-only 8.6.8 version.  Falling back to the old, buggy Apple-supplied 8.5.9 versions, the tooltips do appear, which I assume is what is happening on your system.  I was also able to test with an X11 Tk 8.6.8 on macOS and there the tooltips *do* work.  So, it appears that somewhere between Tk 8.5.9 and 8.5.18, the behavior of tooltips in Tk's macOS Aqua Cocoa implementation has changed. Suggest you pursue this on the Tcl/Tk project's Tk issue tracker (https://core.tcl.tk/tk/ticket) and/or its tcl-mac mailing list (https://sourceforge.net/p/tcl/mailman/tcl-mac/).  It might help to have a pure Tcl test case.  Good luck!  (Nosying: Kevin Walzer from the Tk project as a heads up.)