> Simply uncommenting that works perfectly on Ubuntu 20.04 and Windows 10.

I can't remember the details, but I don't think this worked if the Tcl interpreter had been garbage collected before the Python interpreter shutdown. Therefore, Tcl_Finalize (or similar) would preferably be called at Tkapp dealloc, but we cannot do that because the user may create more interpreters later. I will try and give a reproducible example when I have time.