Fixed size Widgets do not resize correctly on DPI change

Reproducible on Windows 11

Version 10.0.22621 Build 22621

Setup:

Display 1 (Primary): 100% Scale - 1920 x 1080

Display 2 : 150% Scale - 3840 x 2160

Steps:

Move a fixed QWidget with no parent to Secondary Display

Change scale on Display 2 to 100%

(I don't think multiple monitors matter, simply switching DPI causes it)

Expectation:

Widget resizes correctly to the lower DPI

Actual:

Does not resize correctly.

Fails in both directions 100% -> 150% and vice versa.

EDIT: Sorry this might not be the the exact root cause, but without a resize the widget doesn't render correctly

Root cause:

On a geometry change event following a DPI change, isResize will never be true for fixed size windows.

QGuiApplicationPrivate::processGeometryChangeEvent(QWindowSystemInterfacePrivate::GeometryChangeEvent *e)

https://github.com/qt/qtbase/blob/68ae776e73881cbc160cd747e401631452e7f659/src/gui/kernel/qguiapplication.cpp#L2702

Minimum reproducible example provided in WindowsDPI_FixedSize.zip

Note: In cases where windows are not a fixed size there always seems to be a minor difference in actualGeometry vs. lastReportedGeometry on a DPI change.

Worth investigating on its own