Hi,
As melmarker saed if you add lxqt packages over kde you will have a mixed qt4 qt5 environment and it might be problems.
I will try to install in a vrtual machine a mixed env lxqt and kde to see if are problems.
Tough if you want to do this you need only to run :
addpkg lxqt
over a dist-upgraded kde install.
Thank you.