Qt6ct dark themes are broken and hard to read

First, IDK if the component is "active Qt" exactly. I couldn't find a component "qt6ct", so I chose "active qt".

When you run qt6ct and choose "darker" theme and then run any application that uses qt6, part of the texts are black. Which on a dark background is very hard to read, nearly impossible and eye-straining.

This particular screenshot is from mkvtoolnix-gui but the same problem occurs with other applications as well, such as qbittorrent.

For comparison - there are no black texts in "darker" theme when the app is using qt5.