Reproducer attached. There is a QMainWindow acting as top-level window. And a QWidget parented to QMainWindow acts as child window. QWidget is assigned a QHBoxLayout in which a QLabel is showing a string.

The issue is that QWidget is not minimized to expected position. Although being at lower-left corner above Windows Taskbar, the minimized QWidget is offset upward by certain amount. And 2 changes can make QWidget be minimized to expected position, i.e. right above Windows Taskbar with no gap:
1. Do not use layout inside
2. Do not setWordWrap(true); for embedded QLabel (this is quite weird)

A screenshot is also uploaded to illustrate the idea of "offset upward by certain amount". See that there is a gap between minimized QWidget and Windows Taskbar. With either 1 or 2 described above that gap is gone.