It is widely documented that the default `windowsvista` style doesn't properly support Dark Mode. However, Dark Mode nevertheless causes labels on disabled `QPushButton`s to be rendered as black, making them hard to distinguish from enabled ones. The only other older Qt version I still have installed, 5.15.2, did not have this issue.

This can be reproduced with the TextFinder example project. After unchecking `enabled` for the `findButton` in `textfinder.ui`:

Switching to Light Mode (either between a restart of the program or even while it is running) fixes the button label color:

As does applying the Fusion style via `QApplication::setStyle("fusion");`, which gives the same result in both Light and Dark Mode: