I have tried Q on Ubuntu 22 with Gnome and XFCE. The result was the same: Q does not follow the system theme. So, even when the system theme is dark, Q is white.
Back when Q was using QT5, installing some qt5- package solved this issue, but now that Q is using QT6, I have tried installing things like qt6-xdgdesktopportal-platformtheme and qt6-gtk-platformtheme, but there was no difference. Is there an easy way to make the system theme work? If the method is complicated, I would just give it up.