This only applies to spins before 23.0.3 and the 23.0.3 LXQt iso’s released 10/8/23. A new set of LXQt iso’s was uploaded 10/9/23 that isnt affected by this error.
An upgrade to kvantum-qt5 breaks every theme produced by the SbK project. This is because the package is now kvantum, its marked as providing kvantum-qt5. Instead of removing your theme open a terminal and force the kvantum upgrade.
sudo pacman -Sdd kvantum
Then upgrade the rest of the packages with pamac or pacman as you normally would.