I've decided to try also Xfce window manager. I've also installed power manager, but disabled it and also disabled xss-lock because there are incompatibility issues. Fortunately Xfce monitors the battery with the same icon present in lxqt. I've installed alsa-utils and alsa-tools , remapped some keys to enable audio mixer. For the brightness I've used the script from lxqt, but it only works after I login first in lxqt. Phone ( if xss-lock is enabled ) rings, but no way to work with the silver side button to accept calls. In kde everything works fine. But libreoffice works like a charm without the problems mentioned in lxqt and KDE : Libreoffice is too slow in lxqt and KDE. ( I suppose XFCE doesn't have 3d acceleration ).
So, is there a way to disable hardware acceleration in lxqt and Kde ?
Also in XFCE there is no pop-up message to answer calls in xfce when the phone rings . Is there solution for this ?
Thank you all.