Unfortunately, if you're used to QtDesigner's light theme, which doesn't change even when Windows has a dark theme for applications, the version that comes with PySide 6 (QtDesigner 6.8.2) automatically adapts to the Windows dark theme. There's no option to switch to the light theme without changing the Windows theme. On the other hand, the version that comes with pyqt6-tools (QtDesigner 6.4.3) still retains the light theme regardless of the Windows theme, but with the latest versions of Python (e.g. 3.12 or 3.13) there's an error when running pip install pyqt6-tools (although it works with Python 3.9 if you're interested in that version).