Probably not a Gnome issue but not sure where to put it. As of late I’ve noticed issues with nearly all of my QT based apps not always handling font colors correctly. I use dark themes but there will either be text labels that are too dark on their backgrounds or an entry box that is lighter than the rest of the theme and the text is white as well. This effects appimages as well. I’ve tried changing themes and messing with Kvantum but haven’t fixed it.
Several of us have had the same issue. Here is a thread that covers some of the different solutions we have found to date.
I am still hopeful this issue will be fixed in an upcoming update, but since the problem is with a Kvantum update, we will just have to wait it to be fixed there.
Do you have Qt5 settings (qt5-ct) and Qt6 settings (qt6-ct) installed and configured?