Summary says the issue. There is no error shown, the program just exits as soon as it hits the method call with that specific signature. The signature that is just the ResizeMode does not crash and functions as desired. It is supposedly a supported signature, according to the python type interface file and the error message shown when you give it an actually incorrect signature:

Supported signatures:
 PySide6.QtWidgets.QHeaderView.setSectionResizeMode(int, PySide6.QtWidgets.QHeaderView.ResizeMode)
 PySide6.QtWidgets.QHeaderView.setSectionResizeMode(PySide6.QtWidgets.QHeaderView.ResizeMode)

I tried my best to debug it, but I do not understand how to attach a C++ debugger to the python runtime despite attempting to do just that. I can say that the log files and Windows event state that python crashed, and don't give me a stack trace in C++.

ASSERT: "visual != -1" in file qtbase/src/widgets/itemviews/qheaderview.cpp, line 1239