Prior to Qt 6.5 background for items was rendered only when alternating background for items was specified, allowing QStyledItemDelegate to render background independently. This however was changed by the https://github.com/qt/qtbase/commit/...654e6929fa8987 commit. I've found another commit that is part of this regression: https://github.com/qt/qtbase/commit/...1117a9f9c40421. This one translates PanelItemViewRows into PanelItemViewItems to "properly" render background because it is non-styleable from qss. This causes the background to be rendered multiple times..

One solution would be to override PE_PanelItemViewRow using QProxyStyle but this does not work with stylesheets which is hard requirement as the app (FreeCAD) allows custom styling.

Another possibility would be to set ::item in qss to have no background and somehow render it in QStyledItemDelegate but I don't know how to do it in a way that it would be possible to control it using qss.

Incorrect behavior:
327131420-7922405f-fcbc-41a1-a480-b566228b02d1.jpg

Expected one (like it was in Qt5):
bZNSiwqU.jpg