On Windows, QFontDabase in Qt 6.8 does not list style variants of families anymore. This is a regression from Qt 6.7. One liner to demonstrate the issue:

python -c "from PySide6.QtWidgets import QApplication; from PySide6.QtGui import QFontDatabase; app = QApplication([]); print('\n'.join(QFontDatabase.families()))" | grep -i arial 

On Qt 6.7.2 the output is:

Arial
Arial Black
Arial Narrow
Arial Rounded MT Bold 

On Qt 6.8.2 the output is:

Arial
Arial Rounded MT

Note that Arial Black and Arial Narrow are missing. This means it is no longer possible to select these via QFontComboBox, for example.

Downstream bug report: https://bugs.launchpad.net/bugs/2106504