Is this proposal for porting to wayland/plasma 6 or upstreaming it to KDE ?
porting to Wayland (but also X11) and upstreaming.
Menwhile, material-decoration with LIM has been upgraded to Plasma 6.3.
Plasma 6.3 has broken compatibility with the LIM.
LIM relied on the windowId() method of KDecoration2::decoratedClient, which is now unavailable in KDecoration3::decoratedWindow.
To replace it, we rely on the internal API of KWin::X11Window, in the hope that the KDE developers will stop making their Desktop Enviroment progressively incompatible with X11.