sudo apt install lubuntu-qt-desktop
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies.
 lubuntu-qt-desktop : Depends: calibre but it is not going to be installed
                      Depends: fcitx-frontend-qt5 but it is not going to be installed
                      Depends: lxqt-about but it is not going to be installed
                      Depends: lxqt-admin but it is not going to be installed
                      Depends: lxqt-config but it is not going to be installed
                      Depends: lxqt-globalkeys but it is not going to be installed
                      Depends: lxqt-notificationd but it is not going to be installed
                      Depends: lxqt-openssh-askpass but it is not going to be installed
                      Depends: lxqt-panel but it is not going to be installed
                      Depends: lxqt-policykit but it is not going to be installed
                      Depends: lxqt-powermanagement but it is not going to be installed
                      Depends: lxqt-qtplugin but it is not going to be installed
                      Depends: lxqt-runner but it is not going to be installed
                      Depends: lxqt-session but it is not going to be installed
                      Depends: lxqt-sudo but it is not going to be installed
                      Depends: muon-discover but it is not going to be installed
                      Depends: pcmanfm-qt but it is not going to be installed
E: Unable to correct problems, you have held broken packages.