In addition to better drawing of some widgets,
● To support Qt5 long after Qt6 becomes the default, compilation without KDE Frameworks is made possible (if it is used, KWin's blur effect will be available only under X11). It works with Qt6 too.
● Rounded buttons, combo-boxes and line-edits are allowed in LibreOffice.
● Openbox themes are removed (Openbox's development stopped years ago). If you use Openbox, you could import its themes from older versions of Kvantum at GitHub.