KDE 6 Desktop Cube Doesn't Work

I enabled it from Desktop Effects, tried meta + c and install qt6-quick3d package but doesnt work.

Update: Version 6.9.0-1 of “qt6-quick3d” is buggy. It was working in the previous version, but after updating to this latest version, it no longer works.

Solution:

sudo pacman downgrade
sudo pacman downgrade qt6-quick3d

Select the most recently installed version marked with a “-” and reinstall it.

Long live FREE SOFTWARE, long live LINUX!

Edit: This issue was caused by me updating KWin without updating qt6-quick3d. In other words, I had performed a partial update, and I’ve now seen how critical that can be for Arch Linux. Once I ran a full system update that included both, the issue was resolved.