/usr/share/xsessions/QLubuntu.desktop is in lubuntu-extra-sessions 0.46.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 | [Desktop Entry]
Name=Lubuntu Qt session
Comment=A specific Lubuntu session using Qt
Exec=/usr/bin/lxsession -s QLubuntu -e LXQt
Type=Application
|