I use KDE Plasma, which is great, but it always bothers me on the default themes, most third party apps have a different design language compared to the desktop and system apps due to them being GTK and Plasma being Qt. Are there any good themes that can be installed for both Qt and GTK and make the system look as visually consistent as possible? I don’t need everything to look identical, just similar enough that a GTK app doesn’t look out of place when most of the apps I use are Qt.
you can use QGtkStyle to make Qt apps to use GTK style everywhere or use Breeze and Adwaita, that have versions for booth. kvantum is a qt theme engine where you can instaAdapta, Arcll clones of gtk themes, like Adaptation, Maretoa, etc.
Arch Wiki have a comprehensive pqga bout this. https://wiki.archlinux.org/index.php/Uniform_look_for_Qt_and_GTK_applications