The default compilation is against Qt6 now (For Qt5, ENABLE_QT5 should be set to ON), and the support for qmake has been removed (because KF6 doesn't support it). The blur effect of KWin 6.0 is supported.
Also,
● It is possible to reduce only the opacity of inactive windows with negative values of the relevant setting (in Kvantum Manager).
● Added a workaround for a bug in Qt 6.6, because of which, translucent menus might be drawn with wrong sizes after being moved.
● Added a workaround for tiny overlaps between tree branch lines with translucent light/dark colors.
● Added a workaround for a crashing bug in KDE's plasma-settings.
● Added a toolbar, containing a date-time editor with popup and a progress-bar, to kvantumpreview.
● Minor fixes.